Stick with my new partner?

So I'm currently in a situation where I'm now living with my new girlfriend that I love dearly but I'm finding it very hard to settle and move on after the breakdown of my marriage.

I was with my ex for 12 years and married for 6 but this ended 10 months ago (Jan 2017) after some realisation that things hadn't been right for a number of years. We have 3 children together (son 10yrs, twin girls 5yrs) and the stress of life, work and kids (the twins especially) simply got the better of us and we drifted to the point where sex was nonexistent and it became more like a sibling relationship. The split wasn't hostile and we although it was painful, we agreed it was for the best.

The problem I have now is that I moved on very quickly and met someone new within weeks of moving out of the family home. I don't like to think of it as a rebound but I expect that there's some truth in this. I didn't intend on getting into anything serious so quickly but this women made me feel amazing. We have so much common ground and then of course there's the sex... the intimacy that I'd been craving for so long. My ex wasn't the most affectionate person to begin with but this stopped years ago and caused issues within the marriage. Now that I was receiving attention and affection willingly, it made me want more.

At first it worked really well. I have the kids 3 days per week on average. Week one would be two midweek days, and then week two would be the two midweek days along with the weekend. This was perfect for everyone as I got to spend quality time with my children, my ex got her space she clearly needed and then my new girlfriend had time to see her friends and family during the times I had the kids; I, on the otherhand didn't have as much 'me' time as maybe I should've had after seemingly being blinded by this new relationship I had embarked on. Anyway, things worked well for a while and I was happy to have different focuses in my life and things were going well.

After 6 months into the relationship, I needed to look for a new place to live as the tenancy on my new flat was coming to an end. My girlfriend and I had discussed maybe moving in together and the idea seemed like a good one. After all, she'd met my kids a few times (and they love her to bits), I enjoy spending time together and with a joint income, we could get a bigger house which would be great for the kids. After a few conversations we decided to view a property to rent and we instantly loved it. It was exactly what we were hoping for.

So, we moved into the new property in August this year. It was exciting. It was a blank canvass and the kids loved it too.

Once we were in and settled I started to feel anxious. I couldn't put my finger on it but things didn't sit well with me. Things felt wrong at times. This was mainly while the kids were with us. Maybe I was feeling guilty over the fact I'm playing happy families with someone new? As the weeks went on I found it hard to put a face on and it became apparent that I wasn't being my usual self. We spoke and I suggested that it was due to the whole transition and I'll/we'll be fine. I still really really like this women at this point but my anxiety levels are staring to increase massively. Our loving, flirty text conversations became less frequent. Nice messages but not the same as they were. We're now in November and I'm now very confused with my situation. I want to be with this woman but I simply cannot shake this feeling I have. There's a wall up and I'm struggling to bring it down. It's causing an atmosphere no matter how hard I'm trying to mask it. I really don't know why I'm feeling like this. Is it grief over my marriage? Am I feeling guilty? Is/was it too soon?

Right now I feel the best thing to do would be to end things. It's not fair on either of us and clearly things aren't the same as they were but I don't want to lose her.

If anyone has been in a similar position or could offer any advice I'd be very grateful.