Why does my best guyfriend get upset when I choose my boyfriend over him?? (10 POINTSS!!)?

Okay so lately I've been noticing alot of changes in my ex//bestfriend. We went out a while back and seperated because he moved to Georgia and I guess couldn't waitn on our relationship. But during the time period between then and now, we've become bestfriends. No doubt!! But I finally met a new guy and he's awsome! I really like him. Now before we met I talked to my ex everyday and I still do!! But now I'm also making time for my boyfriend and he seems to get a bit upset when I'm talking to him and my bf calls and I have to go. I don't understand. I let him go when his gf calls him and I don't complain. For example, on Valentine's Day my bf had work so I was at home alone the whole day. But after my bestie spent time with his girl he spent the rest of the day talking to me on the phone. We were going for an all-nighter but my bf called so I had to let him go. He sounded a bit upset having to let me go so I promised him that we dwould o an all-nighter the next day. Now the next day we're off!! We're talking we're laughing and he's happy!((: But I told him that if my bf called I was gonna have to let him go til' later. He kept saying no and that I better ignore my bf's call. So when the time came and my bf called I had to beg him to let me talk to my bf without getting upset! He was furious. I hadn't made him that mad in forever. We hung up and he sent me a text saying "Your bogus yo." I could tell he was really upset. I told my bf what happen and he umes that my bestie still has feelings for me. My bf is studing phsycology and he knows alot but I just don't know. What do you think?? What's your opinion on this?? Please and thanks!<333((: