can someone help me understand

so, i am 15 and i have a boyfriend and everyone who gets to know me usually knows from social media and such which im not bothered at. but i have a friend who is a guy and is asked from one of my friends if he likes me and i heard him say that im pretty but since im in a relationship there's no use in trying,which i was fine with. but why is it that the day after when he saw me, he didnt even speak to me, he just asked me if i was ok? i mean he was a friend whats wrong now?