I see this is your second post here on PC. So welcome to Psych Central. Honestly I doubt any of us, here on PC, are going to be able to tell you if the problems you've had being with a girl you have strong feelings for are related to your mental disability. That's certainly a possibility. But it could also be the girl just isn't into you, so to speak. Or perhaps she already has a romantic relationship established with someone else? Or maybe she's just at a stage in her life where she's not interested in any kind of relationship. There are just all sorts of possibilities here.

What can you do about it? Well... if this girl simply isn't into you, or isn't interested for some other reason, I don't know as there's a lot you can do. I guess my thinking would be that what you can do may be to simply be a friend to her, if you can, & see where it goes... if anywhere. You can't make her want to be with you if she just doesn't. And, if that's the case, perhaps what this is going to come down to is that you may simply need to keep your options open in the relationships department. Good luck with it though.