Why does my husband prefer porn to sex?

I am hoping for a little insight to my problem. My husband and I are both in our early 30s (technically, I turn 30 next month), we have been married for 2 years. We dated for about 3 years in high school, then our paths crossed again a few years later and we dated 5 more years before we got married. I am very physically attracted to my husband and he claims to think I am sexy and beautiful.

This may be a little jumbled, but I'm just trying to type this up fast and give as many details as possible.

I do not have a problem with my husband watching porn; I am not a hypocrite and totally understand that sometimes there is a need to just handle things yourself. It's natural and we all do it. With that being said, I do have a problem with dating and sexting sites when you are married.
In the past two years my husband and I have had a few hurdles: I have a mental illness that sometimes makes me hard to live with (I'm sure), I had discovered that he was sexting with a coworker and repeatedly attempting to get her to come over and have sex with him during my last hospital stay (to this day, I cannot speak an ill word against this girl without him freaking out), around that time he was also looking up sites like Ashley Madison, although he never signed up. After all that went down we talked a lot and worked through it. He swears that he would never cheat on me and that he never wants to lose me. He cried. He even told his Mother what he had done. I forgave him.
Since then our sex life has gone from 2-3x per week to maybe once (sometimes* twice) in a 2 week period.
After that I decided to focus on becoming more confidant about myself and lost over 60lbs, taking me back down to my high school weight.
I'm glad I lost the weight for myself and not for him, because it doesn't seem to make a difference to him anyway and I would have ended up very disappointed.

A few weeks ago I discovered (on my personal laptop that he uses sometimes) that he had signed up for a sexting site and searched for much younger girls in our area. When I talked to him about it he said that he was just curious to see if there were any good looking women in our area and that he had no intention of following through or messaging with them. I love him, and although I was skeptical, I agreed to let it go and move forward. But the nothing about our sex life has changed. If I try to initiate anything he will either say he isn't in the mood, or respond with "didn't you just get some the other day?". Then as soon as I go to work or sleep he is at the porn. Almost every night.
I just don't understand. I am very adventurous in the bedroom...I am also very giving. I have lots of toys and creams and outfits. I've read so many posts from people with similar problems and tried to take their advice: I've tried talking to him, I've tried being more attentive both in and out of the bedroom, I've tried new moves and tricks during intercourse, I've tried just focusing on myself. I just need someone to give me some feedback. I love this man, and I think he loves me. But I don't know if I can go through life feeling so unfulfilled and unattractive.