negativity

I'm so happy and excited I got engaged yesterday night . My family is so excepting of it and I'm truly bless for that. On the other hand his family isn't . Except  his sister and brother they congratulated us. But his older sister and his older brother. There kinda rude about it . I feel really sad. A knot in my stomach of feeling upset. I've been with my boyfriend now fiancé for almost 3 years now. There upset because we're young . He's 17 and I'm 18 ...I get that .. I know we are young but at the end of the day it's my fiancé choice to even proposed to me . I never beg him or mention it marriage like that . This all came from him and I'm bless . But I'm feelings down . Truly I think we can make it . We're about to graduate. He's leaving to the Air Force once we graduate and I'm following him and still planing to get my degree political science . Any positive thoughts.... feeling sad I turn 19 in April he turns 18 in July