What does it mean when his friends call me his girlfriend? poll ?- does he want a relationship with me?

I've been seeing this guy for 2 1/2 months things are going awesome and I'm like in their "group" of friends now. We spend as much time together as possible. We have not talked about our relationship or anything and I really want to bring it up and make sure he knows that I'm not going to keep seeing him as casual dating. I always get afraid tho and awkward and don't say it. ha anyways, what does it mean when all of his friends assume/apply we are dating. his friends will call me his girlfriend even when he's standing right there. also the other night I was driving his friend was in hte back and he was in the passenger seat next to me and his friend was like so has he met your parents yet I bet they hate him (he was joking haha) and my guy was like no but they love me. also the other night his friend was like "are yall brother and sister" to us and I was like what? and he was like "yall look alike" and then started laughing and was like "hahaha I'm joking but haven't you always thought it'd be funny to walk up o a couple and ask if they are brother and sister?" me and my guy both just laughed. does it mean anything that all of his friends think we are in relationship and that when EVERYONE we know treats us as if we are in a relationship and say things openly to us about us boyfriend/girlfriend and it not really being awkward? what does this mean? believe me I know I have to communicate with him we are mature adults and it is ridiculous that I have not been able to just straight up ask him but I think I'm afraid to lose this great guy that I've finally found. I don't know really why I can't bring myself to talk to him but I just wanted to know if this meant anything at all. also any tips on talkin to him about what exactly he wants we've never talked about us but I am 100 percent positive he is not seeing anyone else but that does not mean we are exclusive I just really need some tips on how to make sure I don't say the wrong thing and piss him off I tend to not realize that I get aggravated sometimes with him (really tho its me not communicating not him doing anything wrong and I've really worked on that and improved) but please some one (preferably guys answer. by the way I'm not sure he's ever been in a serious relationship he's not a player but he's not like mushy and super romantic and always kind. he's always sweet to me but he's not like labeled a "nice guy" so someone that seems like him please help) let me know if it means anything about his friends and everyone else in the world and all that (also his friends love me and tell me how much they like me and how bad ass they think I am and we are all pretty tight considering I hang out with his friends a ton I mean he is always with me haha) and also some tips on communicating with him! thanks yall so much!