I'm not a Marine but I am active duty Air Force, one of the best decisions I've made. And it was totally worth it. Don't let some dumb girl choose your life decisions, if this is what YOU want to do and something you aspire to then do so, if she cared about you and your relationship with her then she'd be accepting and understanding of it regardless of how she really felt, if she did care yea she wouldn't agree with it but she'd still stick with you cause she cares and loves you. Listen to your heart and your guts dude.