I think my boyfriend gave his phone number to a girl last night...wtf?

Yesterday my boy friend told me he was taking his cousin home and coming right bakity amd that he needed gas money we hadn't spent much time since his cousin was over a few nights so I was okay with it. Anyway he left hours passed I called to see where he was he didn't drop his cousin off he had more guys in the truck with him. So I just went to sleep a few hours.later I called him again and when he answered he was like Alright then sweetheart, you got my number ok hello so I get mad like wtf who did u just give your number out to and who are you calling sweetheart. He says baby I'm talking to you which pissed me off more because I know for a fact he was not talking to me he was in the middle of giving his number out when I called him whenever he gets with his cousins he acts different we got into an argument he didn't come home last night he xlaimed his truck was out of gas he was all the way in another city about 20 minutes away my place ni the suburbs just bullshit. I strongly feel when hes out away from me hes sneaking around behind my back and he bals me insecure but h makes