So confused.... trying to deal

My husband has known hes ADHD for a long time he is 25 now, we struggle regularly with this. The way he treats me and doesn't realize it, nor understands why im upset. Recently I found that my husband was talking to a girl online from a game he played quite frequently. We've had issues with the game because it took all his focus but I never imagined that he'd reach out to a female on there. At first, it was that I found naked pics of her on there, and he lied saying he didn't know it was her. Then I found out that it was a girl he ran with in his guild. I was devastated but willing to work things out. We had a discussion and I thought everything was okay he agreed not to talk to her at all anymore and that the pics was as far as it went. The next day I went to six flags with a  girlfriend that had be planned for several weeks.  He called me while I was gone telling me how much he missed me and I needed to hurry up and get home. I really thought that he was wanting to work things out. The very next day hes on his game and I come in the room and see that hes iming with her. He immediately explodes says that he should still be friends with her and that hes leaving. So his buddy comes to pick him up that night. I was so confused, I didn't know why he overreacted or what was going on he compleat shut down said he needed a few days. Well I decided to talk to the female find out what going on. I contacted her on the game and he immediately calls me... She texted him on a cell phone I didn't even know he had. He tells me that hes packing up and leaving me for good. I'm falling apart at this point not understanding at all what has gone on. I had thought we were doing good, I had backed off and stopped nagging. We were arguing less. I contacted the girl again, begging her to tell me what happened. She gave me a one sided story making herself be the innocent though I know they were both at fault. She told me while I was gone at sixflags he got on webcam with her and showed her things and talked sexual, very sexual. That their texting was the same way. She then gave me his cell number. I called him late that night after talking to her for an hour and told him I wasn't over reacting but the next day he will be picked up at work by me, and he was coming home. That day he came back he was distant, and seemed cold more then normal. He stayed at the computer and barely talked to me. Finally I went in there and told him i loved him and wanted to work things out. That I was confused, he told me he was too that he didn't understand why he did it, that he loves me and doesn't want to lose me but the girl gave him a new feeling of feeling special and he wanted to hold on to it longer. I'm having the hardest time getting over it, it hurts so much because I give him my everything and return hes withheld and distant. He doesn't take into account my feelings about things, and thinks that this problem just disappeared the day he came home. I know hes really trying he has blocked her on everything and lets me check all his records, but still the dreams are there and how do I know hes not going to get this feeling and do it again. I just want to reach out to other women who know what I am going thru and that can give me some advice. I dont want to leave my husband, I love him dearly and I know he loves me just as much which makes this ever harder. I just want him to really understand how much this really hurt me, how im falling apart inside but still trying to be strong for him and its not helping me at all