Search Results: lying about having a girlfriend

My boyfriend has been consistently obsessing over this one girl. A female friend who he'd been seeing for ages without ever telling me of her. We've been dating 3 years and I think it's odd for a guy to simply meet with a girl you don't know behind your girlfriends back. I just recently found out he'd been searching for her every single day on Facebook and I was really hurt and upset. Why would you search for someone if they're not in your thoughts?
It's not the first time I've felt uncomfortable with how he is over her so I suggested a break from each other. He says he only wants me and no one else but this is his first relationship. Everything else is perfect and I adore him but I feel like I can't trust him. He's always secretive about her and always gets a guilty look and denies everything even when I know he's lying.
But now I'm feeling guilty over arguing with him and suggesting a break. It's our anniversary tomorrow and all I want to do is see him but I don't think it'd be a good idea.
Do you think I'm over reacting or fully justified in what I've done?

I've liked him all school year. The day I noticed him seemed to be the day he noticed me, too, but he had a girlfriend then (broke up early Feb). He broke up with her using college as an excuse, but she's also a lying slut, so that's a good possibility too. While dating her, his signs were subtle (glances, shoulder brushes, etc). After, though upset, he seemed to step up his signs in liking me. He got back together with her for a week (I didn't know this then) and acted distant to me again. This is my proof I'm not imagining it all. Depending on what's been going on, his behavior varies. There were 2 phases where he became more obvious (Feb and after Prom). After Prom was especially weird. He flirted HARDCORE (for him) and he didn't hide it. Everything he did before, he was attempting to hide it. This time even his friends saw. He blushed whenever I approached him, he initiated random convos, and he talked about me to his friends (idk what he said). Then, he started pulling away. He never appeared to hate me or anything, just like he was trying to distance himself. Last week before he graduated, I confessed. I'll post the conversation below (read that now). Word got out fast because it was a public spot (duh). I'm not being made fun of by the general population (opposite actually, I'm getting pats on the back for having the balls to ask the hottest guy in school), but his ex is trying to make me believe I am. She snickers with her friends when I pass. You know. That jealousy crap. From what I've heard (true or not) he felt like crap turning me down. Just because he's a nice guy? Or because he WANTED to say yes? The two days left afterwards, he was very awkward and was avoiding me. Not meanly. Just... You know, not sure how to act? He pretended not to be interested in me, but I already know he's been on my FB and twitter. His act was see through. So did he mean what he said? Or was he just being nice? Is it really bad timing? Or was he never interested?