I’m with someone but they’re moving too fast for me

I’ve been with my partner for about 6 months now. I have deep feelings for him and he loves me. He brought up the question of proposal but I told him it was much too soon. Since then he seems to be trying to expedite the relationship so that I’ll marry him because he wants to be with me for the rest of his life. But I don’t know if that’s what I want. I care for him but I don’t know if I could love him for life. I’m in the military and at the moment I can’t talk to him because of where I am and I’ve just been thinking on things with the time and space I have. All I can think of is that I might be able to be with him for life but the timing is just wrong. That’s years in the future and I’m in no place to get married at this point in my life. It’d end my career. Lately there’s someone else I’ve been talking to and confiding in- not romantically. But recently I’ve been feeling closer to this person and he has hinted at an interest in me.. I don’t know if I’m starting to feel things for him or not but I’m confused. I know I can’t continue on in this relationship if I’m pressured into it. But I do truly care for my boyfriend. But at the same time I might be feeling something for someone else. I’m young and I want to be able to live my life and experience things before I marry, especially considering my career. I’m constantly deployed and I don’t think a marriage this soon in a relationship would last. What do I do?