not wanted by my bf?

Why is it that every time I'm out somewhere, I see couples holding hands, laughing, kissing and hugging. Or my friends and their bf/gf and they always show affection towards eachother. now with my bf, he'll hold my hand and stuff but he doesn't like come up behind me and hold me, or kiss me, or put his hand around my waist or any stuff like that in public. and I'm not saying I want to like do a total make out love session in front of people, because I don't like when people do that either. but a kiss now and then, and some affection in public to kind of show me off to let everyone pretty much know that I'm only his kind of thing. because there are times when guys legit come up to me and start hitting on me in front of him and it makes me feel uncomfortable. and I've tried to get him to show a little PDA but he doesn't like to do that.. and I respect that he doesn't like it, but it makes me feel.. I can't find a word for it but hopefully you know what I mean. help?