How do you get over resentment?

My bf & I had been dating for 2 years. We had some problems and he broke up with me in January. We both started dating other people and I started having problems with the other guy due to him comparing me to his ex. Besides, I still loved my ex. Around the ends of March, my ex (now bf) begged me to go watch a movie with him because it’d be the last time we’d hang out since he was leaving to basic right after graduation. I agreed, afterwards I told him it was the last time we ever talked. I didn’t want him to contact me even after he returned. He told me he couldn’t promise me & spent the following weeks taking me out trying to get back with me. He left the other girl & asked me back out some time later. I said yes, but I was afraid he’d come back from basic training as a different person with different feelings. I did not want to go through that heartbreak again, so I rejected him & said let’s just remain friends until he returned and I knew he wanted it. Well time passed and we only grew stronger. He bought me a necklace and a ring, then proceeded to spend the last weeks going on little adventures or just hanging out with his friends/family.

Here’s the problem. I resent the fact that I wasn’t part of the important moments in which he decided to join the military and swore in. I’m sad/jealous that his ex was the one that got to live those moments with him.. I’m the one missing him while he’s gone. I can’t talk to him about it because he can’t have his phone.