MOM VS MY BOYFRIEND!!! NOT COOL!! HELP!

hey! ok this is the situation, my mom and my bf dont get along very much bec he wanted me to move to NY w/him bec he has a great job & apartment, his 19 & i'm 18. we are engaged to put it that way, we wanted to move together but my mom disagreed bec she said i was 2 young and thta she didnt approved bec she didnt know him back then, but they met each other & things arent that bad, so, just 2 make my mom happy im gonna stay in my hometown Puerto Rico and study 1 semester here until Dec, then in Dec i'll be moving w/ my bf 2 NY, meen while my bf is gonna be traveling from NY to PR to c me 2 weekends a month!. But before i move we're getting married first. we wanna settle down cuz i cant have a LDR, i'm gonna keep studying and hopefully make it 2 the end! but truth is that i'm affraid when i leave to hurt my mom, i dont wanna c her sad, but i think that by the end of this yr she has to let me go and let me live my life. its not that im gonna cut up communication w/ her or anything! so what u guys think, is it ok 4 me 2 go by Dec and be happy or stay 4 yrs more until i finish my bachelors Degree!? feel free 2 drop ur opinions! thanx