Search Results: best friend has annoying girlfriend

So my girlfriend (let's call her M) and I have been going out for about three months now, and things have been great. However, my best friend/first-cousin (Z) is really irritating me with how he's being about the whole thing. One of our friends (let's call him C), who happens to like M, has talked to Z about how he likes M, but he's only met her once. Long story short, Z keeps trying to plan stuff where both M and C are invited. Like, I'm not typically the jealous type, but he knows that I wouldn't like it - he never tells me about these plans; M usually tells me that she was invited. M has never been able to make it to any of the parties or movies, but there's one today, and I think she's going. We've been going out for a bit, and I know she's serious about things with me, but it's still annoying. She's totally in the dark on the whole thing, so she doesn't think anything of it. What do I do? I've never talked to Z about how it's frustrating to me as his best friend that he's trying to pretty much set M and C up, knowing how strongly I feel about her. I feel like I should just drop it, because I'm being jealous, but I just expect more from him.