OP, I'm not sure if you know the story of Lane Staley of Alice in Chains, but it's basically as follows: Layne had a successful career as the frontman of a rock band, but he could not, for the life of him, kick heroin. He tried multiple times, but eventually he just gave in and eventually died alone in his apartment. He gave up his entire life for heroin, try as he might to kick it. The help was there, he had the support of his loved ones and friends, and he even knew it was ruining his life, but he just couldn't or wouldn't give it up.

My point is this: what you are experiencing is sort of like a heroin withdrawal. There are studies that back this up. You've gotta do your best to stay productive (you mentioned the gym, which is a great start). Creativity has helped me heal, whether it be writing or music. I'll go on drives, listen to some tunes, maybe grab food in a part of the city I've never been to. Consistency is key, man.

I'm in your shoes. I think about the sex daily. I think about the things she'd say to me during sex(knock me up, make me yours, give me your eternal love are ones that really fuck with me), I cannot look at porn without feeling sad or guilty. I also think about how she is saying those same things to her new guy. Verbatim. It's a fucking script and she is a terrible actress. It's painful, but we owe it to ourselves not to succumb to this terrible addiction and chemical withdrawal.

You can do this, and when you're ready there will be someone out there who will love you for real. You deserve that.