How do I choose between my ex and current gf?

GIRLFRIEND HELP PLEASEEE!! Okay, So about a year ago I dated this girl Morgan. I have known her scince we were both kids. We go together right after my little brother died and she helped me through and was an awesome girl. We dated for a year and half and it was amazing. She took my virgintiy and i took hers. I experienced all my firsts with her as did she with me. We got along and went to school together but she didn’t graduate witch caused conflict. Towards the end of her senior year and my jnior year we started fighting a lot because of her leaving and because she didn’t graduate. Well we broke up right before summer and talked a little about getting back together but never did. We also never did anything sexual over the summer. After that we never really talked over the summer. Once school started I met this Girl named Emilie. She was dateing my cousin, and they had been together for a year and a half. Me anf her had talked before both of us got in to relationships but nothing happend. Well her relationship was on the rocks and while her and her boyfriend were on a break we started tallking. A day later i snuck over a couple nights over the week and we slpet together. Not sexualy but next to each other. The only sexual thing we did was i rub her down there through her yoga pants. Anyway, after about three days she broke up with him and we started going out. Everything was great and we got along amazingly, but I stillt thought about my Ex Morgan a lot. After about a month I started learning her past. She wasn’t a virgin, her ex had takin that and they had lived together. She was quite experienced at 16 and I wasn’t in to that at all. At this time I was 18. At three months is when things went to *. In the first week of Emilie and I’s relationship I talked to two girls on Facebook. We were talking about doing sexual stuff but never did. After about two days of that I felt guilty and wrong and stopped. I dropped both of them and devoted myself to our relationship whole heartily. At three months had suspicions of her talking to her Ex bf and started to persure things people heard from other people. IN the middle of trying to find out, I asked for her Facebook info and I gave her mine. I had forgotten to delete the messages between the two girls and she found them. She broke up with me, posted how big of a cheater I was on facebook, told her whole family and ex and made a huge deal out of it. After a week we got back together and I busted on building trust up with her. In this I dropped the concerns I had about her cheating. On the night we got back together her Ex bf got jumped and was put in the hospital by his new gf’s friends and family. The next day I got a call from one of my friends who was there when it happend and help beat his *. he then told me that her Ex bf went out to the car to get something and his phone went off. When she opened the message it was from Emilie my gf. SHe found out that they had been talking the entire time she was dating him and I was dating Emilie( three mounts in total). A lot of it was sexual and about how much she missed him and wanted him back and wanted to dump me. She was also sending his nudes. When I learned this i confronted her, she admitted it mostly but not the sexual part. I didn’t break up with her, I told her not to do it again and to stop talking to him. She agreed and we stayed together. This was also after we had made love at least five times. We are now at 5 months and my trust is going out the door. She has changed and I have to, we trust each other but not like I want it, but she has turned around and become a 10 tomes better gf than she was. I am currently depped in to The United States Marine Corps on active duty and leave for Recruit training August 11th. I will be gone for almost an entire year doing schooling and training and I dont fell she is devoted to me. She also wants kids and I recently found out that I am infertile and I haven’t told her yet. Here is my struggle. Morgan I have known forever, she was my first for everything and I know would NEVER ever cheat on me.I still love her and I miss her alot. She would always be there for me and is 18 so she could come see me and stay with me. I dont trust Emilie and she lies. She just turned 17 and has a year before she can see me if not longer. She is very immature and selfish sometimes and has a past that I am not comfortable with, but at the same time I love her. She is very nice and has done a lot for me. She is trying to change and I can see that I just dont know if its enough. I need a girl I can trust and that will support me while I a defending my country. Any advice? Please.