Tila Tequila

Best friend and Girlfriend getting close?

Ok so heres the background me and this girl have been dating for 5months now we are both crazy for eachother and we never fight always having fun etc. we see eachother 2-3times per week and other days we skype / phone eachother.
my best friend has also known her for about 4months now and hes a funny guy abit of a flirt but lately its been getting on my nerves he calls up my gf everyday like even when he met her he only called her 3times a week, they were good friends but lately he calls her 2x a day(talks to her like equivalent of me and her talking over a day) and its frustrating me so much,they both flirt with each other alot my gf is a nice girl not some trashy girl but i have bad feelings about this but i act like it doesnt bother me or affects me (im not the type of guy to show to much emotion) im to proud to say anything my gf and friends think im so alpha male (closest thing to describe me i guess.) and yeah i dont know what to do should i just let them keep being like this talking heaps/flirting?? i know if i talk to them they will think im a B!t%h /jealous type i dont want any of them thinking that im weak. or do i have to just talk to them ahh im so confused will be happy for answers thanks (ps both 18 and also think they both dont realise what there doing)