My girl asked my mate to give her his number twice. He calls her at about 1am and ….

I started dating my girl about 6 months ago and things were great until I introduced her to my bestfriend. He used to tell my girl how she wished all other girl he dated were like my girl and he brags about his house and car and my girl kept reassuring me that she is not like that. We go to his house and he would be talking to mainly my girlfriend and tells her that he would prepare or give her anything she wants. About 2 months into the relationship, my girl added him on Facebook and asked for his number. She said she had her reason and I would see in the future. They communicated a few times until I found out about it and she deleted his number and said it won’t happen again. Last month I asked for a break as she said I meant a break up and the same day she asked my bestfriend for his number and they spoke on the phone that night and messaged each other a few times after that. We got back after 3days and they continue to talk to each other. He even calls her at about 1am early in the morning and they talk for more than an hour while we are still going out. Just about a week ago, he told my girl that he’ve not been very forward as he wanted because he met her through me. She never told me any of this, I found out myself. My girl said she will write to the dude (my bestfriend) and ask him not to contact her again and tell him that we are back. I told the dude that we are back but he still kept contacting her – she wrote the message and sent it only to me as the dude said he never got the message. Then I asked my girl to resend the message but she slyly refused to do that up until now. She has got 2 phones and I told her she shouldn’t contact my bestfriend with her other number that it would break me if he has her 2 phone numbers. Lo and behold I went to her phone this morning and I saw that she has been communication with my bestfriend on other phone that I told her not to contact him with until we figure this whole thing out. And he called her at about 1am last night again.
If you were in my situation, what are you going to do? I want feedbacks from both male and female. Help me out guys!