Do you Think I may be Posessive.

So, there's this guy I have been seeing about three months now, and that may not sound like a long time, but in comparison to his other relationships, it is (were talking about a week tops).
He is good to me, he never talks down to me, and I know if I have any doubts I can talk to him about them and that leaves no room for any kind of arguments.
But recently, He has been compulsively flirting with other girls.One in particular.
This girl is my best friend and is currently DEEPLY in love with someone.
Funny thing is, my guy and this someone have a rivalry and they HATE each other, but wouldn't know what to do if the other left. so the Insanity will be infinite.My friend and I unfortunately get put in the middle quite often.
He calls her every other night , and Usually calls me only if there's something wrong or to say "Merry Christmas" or "Happy New Years" ,which is sweet,
Its the fact that I am a jealous person by nature and when he does something that I get jealous over , I feel guilty.
I understand that guys need their space. that why most marriages fail is that they are SO in love with each other , they're always together and so they know everything there is to know and the relationship gets boring, because there is nothing new to learn. But should I feel like thats being taken advantage of?
I mean its not like he completely ignores me, its just it seems to be more attuned to her.
Another issue we have is MY age. Legally, we cant do much because State law says I cant give any kind of sexual consent until I'm 16 (another ..10 months away).
Why does the law matter?
His mother has some giant bug up her arse and would turn him in for statutory rape.I've never met the woman, I don't know why, but she would. ( I would hope that shes just trying to protect him from the Dumb asses that are too fucking stupid to invest in contraception and get preggers, not saying that sex before your a certain age is wrong, I'm saying that if you wont use a rubber, at least, then you have no reason what so ever to cry when that stick is blue, your own fault)
But the sweetest part about it is that he said he could wait and other than his flirting around, he hasn't give me any reason to doubt that. I just wonder if I may be overreacting when I get jealous of my best friend when he calls her more often.