Student Exchange Programs

my first serious relationship was long distance, i live in the US and he lived in England. It lasted for two years and i think most of the issues was the long distance. first he visited me for a week, then i went there for 10 days, then he came and lived with me for 2.5 months and then i went to live with him for 6 months. each visit was wonderful but i knew i would eventually have to go back home. then my second relationship was not necessarily official but a similar situation occurred. i dated a guy for almost 7 or 8 months. we met at school but he was an exchange student. i knew that eventually at the end of the semester he would have to leave but we still thought maybe we could make it work. he went back home and i even went to visit him for about a week. it was all wonderful, but again i left to go home and he stayed there. due to his issues and mine the long distance could not work. now i’ve met an amazing man who i started dating 3 months ago. we actually are from the same town and went to high school together never really having any interest. but… he is in the marines, in california and i am on the east coast. the long distance is working for now and hes coming home soon for about 10 days and then i will visit him for 2 weeks. but again, he is leaving to deploy for 6 months with limited contact. ive obviously done long distance and i feel like we can do it because he is completely opposite of what ive ever been involved with. why do i keep going in these circles? why do i date men who i know are leaving? what is the reason? i want to say i am beginning to fall in love with this man but he has a few more years of service and i would have to move my life for him at least for those few years. is this another lost cause? someone figure out my head please????