What should I do

I am a 21 year old college student thats in love with a man with a fiance of 15 years but she is in the military…and she keeps renlisting back in..they see each other 3 or 4 times a year…but I only have 2 years on it…but he told me he was in love with me..I have never asked him to choose but the feeling are getting so deep..I think he loves me…I can see myself being with him…we are always together he treats me like a lady…every time we say we are gonna take space we end up rite back together again…I just don’t no what to do…I love him so much…I even turned down a good guy for him…he no that he has a problem with women but im just wondering if I stick with him through this what happens when she comes back from over sees…im so confused…some body give me some advice