ADHD Partner's obsession with sex and certain body types -- will I EVER be enough for him?

I'm new here, but I'm very glad I found this site.  My partner of 6 years has been diagnosed with ADHD and OCD.  This was long before we met, and he's under a doctor's care and taking medication.  

We have a HUGE issue like a wall between us since we met -- he is only sexually attracted to women who look a certain way.  To get his "fix", he looks at porn pretty much every day, one woman after another after another, often for an hour or more.  It doesn't matter if I'm home in the next room or I'm out of the house.  He says it makes him "happy."

The problem is that he will not be intimate with me.  In fact, he outright refuses.  We have never had sex once.  I've never seen him naked and he's never seen me.  He's made it abundantly clear that he is NOT interested in looking at me or even trying anything at all and he blames it on my weight.

Now, when we got together, I'd just lost 40 pounds.  I still had 30 or 40 pounds more to get back to my pre-baby weight, but I looked really good.  I worked out, had lots of energy, and turned heads when I walked down the street.  But it was never enough for him.  What he'd say is that I was "close" to what he can "work" with.  And, when I finally left him in 2011 (I lived separately from him for over a year and just came back last September) he made sure to tell me that he was almost ready to 'get together' with me, I was really close...

I see it as excuses.  And now (and I take responsibility for the fact that I could have handled it differently), I've gained 20 pounds back, so I now have 50 or 60 pounds to lose!  

He used to bring up my weight and how frustrated he was (sexually) pretty much like clockwork -- every couple of months.  Now, I think he's at least gotten it through his head that it gets him nowhere and that I have one foot out the door already.  I've gotten a lot stronger over the past year or so.  He doesn't instigate the conversation but, if it comes up for one reason or another, he'll start in with the "you're not going to do it (lose the weight)".  "You can't.  You're not capable.  We're not compatible."  He claims he "knows" I just don't want to do it and I WILL FAIL because I've failed all along.  He tells me the balls in my court and it's all up to me.  If I lose weight and work out and get "fit", he'll try and see if he can work with me.  He claims he doesn't want a fitness model (like the porn he loves to look at), but I know different.  His therapist even told me that only about 25% of the women in the world would fit my b/f's criteria for attractiveness.

I know the porn he looks at because I've become so distraught I've been looking at his computer history.  I know he has a profile on one of the adult hook-up sites, too although he doesn't seem to be too active on it.  And the women he looks at aren't perfect!  They're chubby, some of them.  Some look sort of like me.  But I also know he's really into body symmetry -- the length of the leg in relation to the torso, the size and shape of the buttocks in relation to... whatever.  I don't even understand it.  It's like he's engineering what he likes -- like he's trying to improve upon and engineer ME.  It just seems so impersonal and objectifying.

He told me once that he had to look at porn so he'd be interested in sex at all.  He used to tell me he was doing it for "us".  

So, I guess I actually have two questions:

1) Is his obsession with certain body types -- and his complete rejection of me because I don't fit in with his idea of attractive -- a symptom of his ADHD?  

2) Is his rejection of me sexually because he's impotent (he is, from his medications), because he really can't "work" with someone who doesn't look a very certain way, or because he does not like to be touched????  Is his ADHD making him grossed out by real, physical sexuality so that he'll only get his sex from porn/masturbation?

Sorry for all the questions and the long post.  I've been trying to determine if there's any hope in this relationship at all.  Should I leave? or should I stay? are the biggest questions on my mind.