I cheated on my boyfriend with my boss - then found out he'd cheated too.

I'm confused and could really use some advice on a complicated situation.

I've been with my boyfriend for nearly 3 years and everything has been almost perfect - we met a few months before and the attraction was instant.

When we did get together, it was arguably the best relationship I've ever had. We were obsessed with one another - still are, in almost every way. We booked holidays and went on adventures. He was kind and gentle and sweet, and always put me first (still does). We spoke all day, every day, even when we weren't together.

He's always been quite shy, and I'm essentially the opposite, so I think I helped to bring him out of his shell - he tells me all the time he's never had an emotional connection like this one.

But he was so insecure, right from the get go. I think he worried he never deserved me, but he never realised that I felt exactly the same.

I don't think I helped this, looking back.

In the beginning I was having a strange crisis about my stance on monogamy, and whether or not it was okay to find other people attractive while in a relationship - something I've always wondered about.
I began to realise having an attraction to someone meant nothing if you had no interest in them emotionally. Not that this excuses cheating, but helps to explain what happened next.

He was always very uncomfortable talking about other people being good looking, or even attractive, despite how I told him I found it totally normal, and that if we could speak about these things and be frank about them, they would never present a threat to our relationship.
I see now that this was my part in pushing him away, or making his insecurities grow deeper; he became worried I would cheat.

I told him not to worry - I was always 100% honest with him. But I don't think this helped. He hated that I struggled with the idea of 'true love' and that I thought it was normal, healthy even, to admit we were only human and being attracted to people was okay - as long as we didn't act upon it.

It became a strained conversation, so we stopped talking about it, and, I guess, stopped talking about quite a few things. It drove a tiny wedge between us - and I say tiny because we were still, otherwise, pretty perfect.
Over the next couple of months, however, he gradually became more paranoid. He would ask me questions about who I was with, what I was doing, annoyed at male colleagues and friends who would show a little too much interest, or just be too nice.
It started to get on my nerves - we argued about it a few times.
He made me happy, why would I stray?

Anyway, this soon became an issue. I felt our connection lessen and we began to drift apart.
We had a huge argument after I caught him flirting with a barmaid when we went out for drinks - or just being overly nice, I'm not sure. But I brought it up in jest (a mistake, I see now) and he became angry and told me it was nothing.
Later on that night I saw a message from her pop up on his phone.
When I asked him about it, he said he had only apologised to her for being so drunk. I asked him to show me, and he said he'd deleted the message because he was worried what I'd think. This set off some alarm bells; and it was sort of a downward spiral from there.

Now, please bare in mind - he is one of the nicest people I've ever met. Everybody loves him because he is so sweet, and thoughtful, and generally nice to be around. I honestly didn't believe he had a bad bone in his body, so this raised a lot of questions for me.
It made me question everything I thought I knew about him - was he just portraying himself to be this person, and was really someone else underneath?
Maybe he was so jealous and insecure because he knew he had the ability to cheat himself, or at least the ability to lie to me - maybe I had been completely mistaken in assuming he was always the perfect gentleman.

Of course, it was eventually these questions that started to eat at me. It became so bad, I decided that I was going to break up with him, but struggled with it so much because I still loved him very deeply.

Then I made the mistake I said I never would - I slept with my boss.

I started a new job a month or so prior, and we immediately hit it off as friends - nothing more, really.
But my relationship with my boyfriend became so strained in this month that I guess I'd been seeking conversation elsewhere - something my boss had provided. It just happened one night when we stayed after work for a few drinks (we both work in a bar).

I felt so awful, I broke up with my boyfriend the next day.

He deserved better.

He took the break up incredibly badly, refusing to leave my house because he didn't want it to be the last time we saw each other - it was equally as hard on me, knowing I'd only done what I had because I felt so accused and it had pushed me away; that it had meant nothing and I was perhaps looking for a reason to leave the relationship. I still loved him, I had just messed up - and there was no fixing this in my eyes.

We broke up, but continued to talk. I told him that I'd slept with someone else - not that I'd cheated, but that there had been someone else after. He understood and although he said it was awful to think about, he still loved me and said he could never hate me and it didn't stop him wanting to be with me.

Perhaps a week later, I found out from a mutual friend he'd slept with another girl - almost two months before.
Just after all the arguments and the jealousy and everything that had driven us apart. We'd obviously both had the same drunken and unforgivable idea, to some degree.
The only difference being that he never told me, or attempted to fix it.
Which was perhaps the hardest thing for me to accept.
Did he not have enough respect for me to do something about it?
I understand that it was meaningless, a one night stand with someone he barely knew, which made it less awful than what I did with my boss, as we are actually quite good friends. But the idea that he did nothing, and went about as normal after is driving me insane.

I confronted him, of course - we spoke for hours.
He admitted it all and apologised and said he had caused all this mess with his jealousy and paranoia, and become the person he hated the most.
He said he would never stop loving me, and that he apologised for everything and wished things could have just been different, that he'd been a better person.
Of course, I also still love him - otherwise I wouldn't be here.
I really do think in a lot of aspects that I forgive him, and understand his thought processes. He became so sure he would lose me that his insecurities about our relationship got the better of him; just as they had with me.

The only thing I struggle with is that he swept it all under the rug, and truly hoped I'd never find out.

We fell straight back into each others arms when we saw each other next, and spent the best part of our week off after Christmas talking it through - arguing, crying, hashing out our emotions. Perhaps moreso than we had since the beginning.
In a lot of ways, it's brought us closer together, which I realise is strange.
He wants more than anything to start again, to be better and grow and for us to not to take each other for granted.
Like I said, despite all this, it had always been perfect.

But I'm scared.
I'm scared we'll never fully be able to trust each other, or that I'll always wonder if he is the man he appears to be, and not something else entirely underneath.
I so badly want to believe things will be okay, and that once we've addressed the insecurity and jealousy and really, the only issues that pushed us apart, we can get past this and carry on stronger.

But how can I know? How can I know that I'm not just making a terrible mistake, and setting us both up for failure? The worst outcome of this is that we both end up hurt again. I want so badly to avoid it I can't help but think it might be best for us both to move on.

I need some advice. Some experience in this or just an outsiders perspective.
Is it possible to get over something like this? Or is the damage we've both done irreparable?

Will we ever really trust each other again?
Am I just kidding myself in believing it was only the insecurities and the state of our relationship that lead him to do this, and hide it from me?
Or is there really a part of him that's capable of these things, even though he says otherwise.

I know he's never done this before, or so he's told me. He isn't a serial cheater, and has always believed in good relationships.
I accept my part in driving him away, and he accepts his part of being overly jealous not helping.

But is it enough?