feeling low today

So today marks one of the lowest days I have had in a while. I get a long text message from my gf today. She thinks I have been cheating on her. We have had a great relationship for 8+ months now. We live together, took a vacation to Hawaii together, and we are possibly moving there within a year from Maine/New Hampshire. 
Here's the down side. I am an Aspie, I am high functioning but I still am learning coping skills. I have known for about 4 years. The other night I said something that I didn't realize was hurtful. I realized it the next morning, but never said anything. The text was my gf complaining about that, the fact that I hide my friends on fb, and she believes I was still on a website looking for a companion. The last being the most confusing one of it for me. We met off a dating site. We had struggles in the beginning with trust. (she lied twice about being on after we were exclusive). I forgave her - fast forward to today. I did still have a profile up on another site. I was on two sites when I met her, canceled one & forgot the other. One of her friends saw that profile & thought it was current. After finding this out from my gf I did some digging to find out which site it was, and deleted it. I love her to death & don't want her second guessing it. I have been completely honest with her, but I feel she is very hurt. I am sure she will have a problem believing me from now on. I never wanted to hurt her in any way, but it seems I find some way to mess it up, or something from the past comes back to haunt me.
 
I left work early, came home to talk it over with her person to person. I have no clue what to do, but just tell her the truth over & over. All I do is work & spend all my time with her. She is my counterpart. WTF do I do!