So a few days ago I found out that my boyfriend (of 4 years) has been facebook-messaging a girl that he met when he was at a shop were a friend of his works. I didn't think anything of it when he added her, as it is just something he usually does. But because he seemed to be quite absent the past days, I decided to ask what was going on. As the girl from the shop was pretty much his type, I kind of had a hinch that something might be going on..
At first he lied to me but then he eventually showed me the 3000+ fb-messages that they exchanged over the course of the last 5 or 6 days (talking about personal stuff too, like how many sex partners they had etc.). She was flirting heavily and even though he told her had a gf that he loves, she didn't seem to be bothered by that..quite on the contrary. They eventually exchanged phone numbers and also e-mail adresses.. he pretty much encouraged her behavior. They decided to meet a club, that he usually goes to with his guys, last weekend. And even though that never happened, I can't help but to ask myself if he was about to seriously cheat on me. He claims he just wanted to talk to her and nothing more, but honestly: do you really need to give out your personal phone number when you're in a relationship and exchange that many messages on the internet? I'm pretty certain their little fling would have continued on forever if I hadn't found out. I'm just hella pissed and don't know what to do about the situation. He broke my trust and I eventually told him 2 days ago, that I needed some time on my own to think the relationship through. He begged me to forgive him, as he knows what he has done was wrong and just 'too much', but I don't know if I can 'forget' about this.
How would you react if sth. like this happened to you? What do you think about giving out your number while in a relationship? Any help would be appreciated!