Confused...

My boyfriend and I have been having some relationship problems lately and I need help understanding what is going on.

Let's start from the beginning...

This past weekend I found pornography on my boyfriend's phone. And before you assume I'm a typical girlfriend who spies on her boyfriend, understand the situation. We were in an area where I get poor signal, so I used his phone to look up a car online. Well, when I clicked on browser, the porn website was up.
**Please, spare me all opinions of how you or society views pornography.**
In the past, he assured me that he hadn't looked at it since we've lived together, but that's obviously not the case. I confronted him about it asking why he lied to me. He had no definite answer for me, except that he knew I'd be upset and he didn't want to be embarrassed.

Not a huge deal, porn is porn. But it made me think about the fact we haven't been having sex like we used to. We used to have sex 2-3 times/week, but now we have sex maybe once/week or once every week and a half. Anytime I approach him or come on strong, he almost always says, "I'm tired." He has time and energy for all the activities he wants to do, but when it comes to sex, he rarely has the drive or motivation. I've tried everything from being very sexual, wearing revealing clothing, sexy lingerie, making obvious moves, taking it slow, trying to "fuel the fire" in other places in the house, grabbing him sensually, sending flirty messages, being spontaneous... You name it, I've tried it. But no matter what, he's almost always tired. I take pretty good care of myself and show him in more ways than just sexually that I desire him. I also tend to have the sex drive of a male, so I get pretty bummed out when he turns me down. He only seems interested in me when he wants it which is rare anymore. He will sometimes try to have sex with me the day after he rejects me, but then it feels forced. It's as though we have to go at least one week without having sex for him to have the drive for me. I understand that porn takes less effort, less work, but when there's a possibility it's interfering with your partner at home, then I feel there's a problem. Or, I could be wrong and it could be related to something else.

So, not only is he less interested in sex, but he for the first time in our relationship, showed a sign of jealousy possibly...

Yesterday my boyfriend took me to dinner and on our way he told me he checked my internet history. He told me he saw that I clicked on several different pages of male friends. I explained to him that what he saw was my message history (not actual profile views) and that if he really looked at it, he would have seen all of my messages (including ones from females and gay friends) were in that same history. These messages date back to 4+ years ago.

I asked him why he felt it necessary to check my history. He said he was worried because I posted two pictures of myself on Facebook and was receiving "attention for it." The two pictures I posted were from the neck up and were of me with some makeup on. I rarely post pictures (or anything) to Facebook and my most recent profile picture was from 2012. As I stated before, I take care of myself and wear makeup fairly regularly, but because I looked "dressed up," I decided to snap a few shots and upload them.

The attention he was referring to is about the guy who messaged me. I signed onto Facebook and it said I had a message notification. He was looking at my screen when I signed in, so he saw the message and said, "Who are you talking to?" I've never, nor did I, have anything to hide so I showed my boyfriend the message... but he acted weird about it. The message was from a guy I went to high school with. He made no reference to me or my looks, but asked me about my brother playing sports this year. (He is an assistant coach and we spoke last year about my brother playing). When the guy asked me how I was, I explained that I was doing well, spending most of my time with my family and my boyfriend. Again, even though there was absolutely no discussion about me personally, I threw the boyfriend card out there. I do this with everyone I speak to, even women.

My boyfriend explained to me that earlier that day he spoke to one of his coworkers about my internet history. His coworker told him he had been cheated on twice before and that what he saw on my computer was nothing to worry about. What bothers me is that he'd immediately go to a coworker, a guy he's known less than 1 month, about a relationship question/issue without talking to me first. My boyfriend and I have always agreed that we don't speak to people we encounter regularly (friends, family or coworkers) about each other in a negative way because society as a whole is more likely to remember and judge based on negative things, not the positive. (Yes, I'm discussing this in a forum, but you all do not encounter my boyfriend and I personally everyday). And I'm asking for advice in this setting because I do feel it's important to keep intimate negativity from my family and friends. They already try to pry so much into my personal life, so I pride myself on keeping my relationship issues private from them.

So, hopefully the pieces of the puzzle make sense.
1. He's not interested sexually, regardless of my efforts.
2. He's checking my internet history.
3. He's, for the first time, showing signs of jealousy.
4. He's discussing our relationship with someone personal.