Should I confront the girl I think the guy I am in love with is talking to?

[Twinkle Cutie:]]

I am almost 100 percent certain that I caught the guy I had been dating for the past 4 months talking and to another girl. She post on her twitter about how much she likes him and how he is all her's. When I confronted him about it he said that she's spreading rumors and that it isn't true. When I told him I don't believe that a girl would JUST spread rumors like that and that a guy has to be telling a girl something that leads her to believe they actually are speaking on that level in order for her to say that. He is still denying that he ever spoke to her in that kind of way. He told me that he only talks to her on twitter and texts her and he told me that he stopped talking to her. I even asked him if he's ever hung out with her and he denied that too. When I look at he twitter page, she's tweeted several times about how she's with him, etc., etc.

Every time I confront him about the situation, he denies it. I told him that I don't trust him and I want to ask her for my self and he told me I can. Should I ask her? Or do you think he might've gotten to her first and told her to deny it. I had my friend follow her on twitter and she followed her back so I was going to DM her through her page. Should I?

Also, when I told him I don't trust him and I only want to be his friend he told me he doesn't want to be my friend. If we can't work it out he's just going to leave me alone. With that being said should I just leave the entire situation alone? I still love him and care about him. I told him I can move on from this if he just mans up to it and that I wouldn't be upset. But he still hasn't confessed. WHAT SHOULD I DO?