Boyfriend advice please? (guys and girls welcome)?

Okay so lately when my boyfriend and I have been going out, annoying stuff has been happening. One time we were waiting to cross a street and a car full of teenage guys (my boyfriend and I are both 18) was driving by and they yelled "is she your sister?". Another time, we were getting gas and two guys at the gas station (at a pump a few rows away) waved at us. They looked kind of familiar so I hesitantly waved back and glanced away. When I looked back at them, one was holding up his phone and pointed to it and then to me. After both these instances, I blushed and my boyfriend looked rather dejected and was really quiet for the next several minutes. I don't really get it though. I mean, I think he is hotter than I am (and I tell him that he's hot and that I'm lucky to be with him) yet he doesn't really believe me/think he is good enough for me. What can I do to cheer him up/help with the situation/show him that if anything, I'm the one who is not good enough? Because while the attention has been a little ego boost for me (I'm only human), I really want my boyfriend to know that I'm his and I'm lucky to be his. Sorry for writing a novel on this and thanks in advance!!