Search Results: immature around his friends

Here's the conversation between me and guy friends A and B:

A: where's my phone?
Me: here, why do you feel naked without it?
A: no, but I haven't talked to my girlfriend all week (diff school)
B: Fuck your girlfriend!
A: I want to!
Me: ugh, really?
A: you're just jealous!
Me: Totally!
B: yeah, she's totally jealous of your meaningless high school relationship!

Why did A say that to me? Just because I don't want to hear him be gross doesn't mean I'm jealous. Does that mean he's thought about us having sex? He went there pretty fast. He knows I don't want to hear what he does with her but he tells me in graphic detail, anyway. I doubt she knows this. Plus he's always discussing sexual things he's seen online with me even though he knows I don't want him to. Why so much talk about sex around me? I told him we all assume he bangs her and we don't want details. Still he makes sure I know that he got laid over the weekend or how he can't wait to get laid and how he doesn't need to go to strip clubs because she'll dance for him. Or he says, out of nowhere, that she likes fur handcuffs and he talks about eating girls out a lot. Classy!

I have a love life but don't tell my friends about it. Is he just incredibly immature for 18 or is he also saying all this stuff to me to seem studly or attractive? He's very competitive and hates being compared to other guys. He shows off and preens a lot around me, too.