How can I make him interested in sex? Should I blame myself?

Hi so basically I've been with my partner over a year now, he's never been overly keen on sex; he prefers oral. 
​He has an erectile disfunction, when we first got together I didn't know this so I thought he just wasn't interest. About 3 months into our relationship he finally told me and it made me feel a little better ( i thought he didn't want it because he wasn't attracted to my body, just personality). Shortly after he told me, we finally managed to do it and it was amazing! I fell for him a lot with those first few months as he was such a gentleman! He made me feel like I was the best thing since sliced bread. It's true when they say the sex is better when u have feelings for the person ur with. 
​Well about 6 months ago I found out that he doesn't really enjoy sex for more than 10 or 15 minutes otherwise he gets bored?? I've tried spicing it up, changing positions and even role play! Non of it works! It's not a problem with him getting it up much anymore it's just trying to keep him interested, he forces himself to cum after 10 mins; 15 if I'm lucky!! 
​Personally I take longer so it's not offen that actually get there myself, don't get me wrong it's still amazing but a lot of the time I'm left unsatisfied. He loves going down on me, he'd do that for hours if I asked! And he prefers me going down on him.. I don't mind it but sometimes I feel sick or achey and feel bad saying no PLUS it can last up to an hour and a half so I end up in pain or throwing up because of the constant movements with my head so I get dizzy as well. 
​Sometimes he'll sleep on the floor to get out of sex as well an it's starting to worry me. I'd never force him into it but I think he feels bad sayin no as well? I don't think he realises how much it hurts my feelings when he does it.. He's never been a cuddly guy but it's nice to atleast have him next to me! I get really down when he does. Sometimes I find myself crying myself to sleep when he isn't around cause i miss him or cause I need him with me. 
​Am I just a fool? Is there a way I can get him interested? Or could anyone explain what's wrong?