Let him go.
Look, you had doubts about the relationship (at least I'm assuming that's why you had a conversation about the status of it). Most couples hit the acceptance of bf/gf status long before the declaration of love stage, but you two kinda reversed that. I take it that your instincts kicked in and prompted you to have the "relationship" conversation. That was a smart move to make.
The next smart move I hope you make is to accept the answer you got. I have no sympathy for this guy. While he may indeed not "know what love is," that's not what he led you to believe. When you told him you loved him the first time, he should have been honest with you (either told you he didn't understand love, admitted that he only wanted an FOB, whatever...). But he was getting laid, and he lied to keep getting laid. Now that you confronted him with the damage he's done, he's cut you out of his life.
So....he lied, he manipulated, and now he's run away from the consequences....oh, and he has Asperger's. IMO, he behaved the way he's behaved because he's a liar and a manipulator and a load - not because he has Asperger's. He's not the man you though he was; he's not the man you deserve, and again - IMO - that has nothing to do with his neurological status. But now you know who he is, so do what you can to stop feeding the feelings you had for the man you thought he was - that man doesn't exist. You can't have a relationship with a man you can't trust - and he completely violated your trust. Hon, you're going to have to save yourself here, because he won't. Let him go.
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What you feel is what you are and what you are is beautiful...