What shall i do when my friend and boyfriend are flirting?

Me and My Boyfriend was talking on facebook chat and suddenly he said be right back, and my friend was with me that day and she was on facebook too. So yea my BF said brb and after 15-20 mins, he ditched me just to talk to my friend and they've been talking for nearly 2 months...and i got jealous and got angry, and logged off on him and put statuses..what shell i do? i dont want him to go with my best friend :/ I asked my friend if i can read their convos but she snapped at me and refused.