Why'd my bf change soooo much when he got to college?

ive known my bf for a long time, so ive seen him with other girls and stuff and he's told me about them when we were still just friends....but when we went to college (we'd been together for half a year by now) he completely changed for the worse :( in his other relationships/ours before college he was crazy sweet and romantic and would tell me (and his exes) really cute things and wouldnt really show PDA. he'd tell me that he was always thinking about me and other lovey dovey things which i REALLY LOVED. im really romantic so i kind of need someone to tell me romantic things back and treat me the same way i treat them, but he would treat me EVEN better than i treated him.....but when he went to college he started ignoring me and ditching me every single day for his friends. he would fondle my chest in public and grab my and start kissing me hard core when my PARENTS were in the room...which makes me really really uncomfortable. he tries to grab my chest "sneakily" while my parents are in the room too! and it's not like one time, it's about 5-6 times he tries to grab me. :( many times he's pushed me to have with him even though he knows i want to wait until i get married. he's so different. he would never do this to me when we were in highschool. he never EVER did anything like this with his exes. i dont know why he's like this now~ could it be because he joined a frat? i know the guys in his frat are all ist and like to sleep around...could that be a reason? :( this makes me so upset~ i just want the old him back :(