Well I would definately be a little suspicious. Why isnt he treating you with the level of respect a girlfriend deserves? Its ok to have friends of the opposite sex but to always be around and to let that friend invade your time together.

I think a serious talk is due....

A serious talk is definetly due. But I want you to keep one thing in mind. I was the type of girl that all through highschool my guy friends way out numbered my girl friends. I had 2 best friends that were guys. One I ended up dating and the other stayed my best friend for a very long time, although he also had feelings for me. Many years later, I realized I had unconsious hidden feelings for my best friend, while still being with my boyfriend (the other best friend). When having friends of the opposite sex it always complicates things. Even if they say they do not have feelings, they are lieing to themselves! There are always unconsious feelings towards the other, whether they come to the surface or not, they will at some point in time! There will always be that moment that you realize it, but that doesnt mean it will lead to anything. The only thing it will eventually evolve to is having less friends of the opposite sex. When things get serious and you find your true soulmate, having best friends of the opposite sex fades away because it just doesnt work. It only adds temptation and confusion and is a distraction. The best and only functional thing to do is have groups of friends together and only go out together as groups, preferably with people with all the same things in common, currently in relationships or what not, etc. Best of luck.

samwinchester...I have adopted this policy and it indeed works! It keep the connection between the couple strong. Because thats who your best friend should be anyway. To me, as a woman, no other man should be privalage to my secrets. Same goes for my hubby.

Your partner, wife/husband, soulmate should be the closest to you.

they probably mistake them for gf/bf b/c they're always together. how do you know for sure that shes a lesbian.
he sounds immature to me because he should ask you first. he's not allowing yall relationship to grow, sometimes you need some alone time. if he does it again i would get up and leave or voice your opinion about how you dont like the thrid wheel being around all the time. you could be nice about it.
i never been attracted to any of my male best friends, but they always tried talking to me.