Advice please

My boyfriend and I are in the same university but doing different courses so we only see each other after classes, at the residence and on our way to class. Every time i see him from a distance at school, he's either with a girl or a group of girls. He entertains the girls that show interest in him. He has an ex that keeps coming back for whatever reason. He's never cheated on me or atleast that's what i know but he has a past that isn't pleasing and all of these things make me uneasy. I hate seeing him with girls all the time and no matter how much i complain, he doesn't stop. I guess I'm a little jealous or maybe too jealous but that's normal, right?