Leave it mate.
There are plenty of other women in the world I promise. (Even ones who are emotionally stable, and find nerdy fellows with ADHD and Asbergers appealing)
Yes you could do what prox said and beat him up, but honestly, do you really want a relationship where you have to be a jealous ass and beat the snot out of anyone who your girlfriend bats an eye at? I'd steer way clear of any woman who would find this attractive/ acceptable.
She wasn't manipulated into liking the other person. I understand why you might think that, but unless you have conclusive proof that he is physically abusing/ threatening her in order to get her to break up with you, if that's the case it's would be a whole nother matter entirely. But from the sounds of it, that isn't the case. That is definitely a bullshit way for her to break up with you. I know that she made you aware of the conflicts she was having, and it sounds real nice on the inside to be her knight in shining armor to go "help" her with her emotional issues; grand ideas in our heads rarely work out as well as you would hope.
You said you and her both have Asbergers, this definitely complicates the situation. One thing to remember, it's tough to fix something with a broken screwdriver. (yes I just called you a broken screwdriver, I'm sorry)
But my point still stands, it will be nearly impossible for you to help her with her asbergers related issues, when you are in that close of a relationship. Being bf/gf really complicates the hell out of it, and then when you are both trying to "fix" each other is just a recipe for disaster. One of you at least needs some pretty solid and level footing if you want to have the best chance of success. This is something that neither of you have.
If you were just friends, you could have a chance, as you could relate to each other, and help each other through things, but not have it complicated with relationship problems. (If you have romantic feelings for her, even if you aren't dating you wont be able to effectively help her as well.)
I don't know if you will take my advice, I know it is a bit harsh; but I really just wanted to be honest with you. This crap is stupidly complicated at times. And much of my advice doesn't apply in most situations. For example If you have had a long term (5 years+) stable relationship, and this problem just cropped up, it would be a different story.
So, enjoy it for what it was. It hurts, it's lame. But if this is how the beginning of your relationship is going, its not worth trying to keep sailing. The successes and the failures are all apart of life.
