In love with someone but not sure if I see myself marrying them

My SO have been together for a while and have discussed the potential of eventually getting married. We are in a serious relationship and I do honestly love him, but idk if I see myself being married to him. there's really only one thing about him that makes me think he might not be the one, but it's something that's important to me. He's not very outgoing or good at being social. I didn't care at first, but I see myself being with someone who can freely have fun with people like I do, and get along with my family really well. My family loves him but he's not buddy buddy with anyone and he isn't really close with them, which is something I feel I need from my future husband. I wouldn't want to make him change who he is, but sometimes I feel like his anti social behavior is holding me back. I'm not sure what to do about all of this. Any advice would be much appreciated.