Military girlfriend advice!!

So my boyfriend of 5 years is leaving for basic in June and I’ve been thinking about it a lot lately. I heard from a little birdie (his grandma lol) that he’s planning to propose soon and he’s talked a lot about getting married soon after he gets back. I’m just a little nervous bc everyone keeps telling me how much he’s going to change while he’s there and stories about men cheating when they leave. He’s not a cheater and I know that I just hope that the whole “changing” thing doesn’t change his views on his love for me? I know I sound a little insecure and I’m probably just letting other people get into my head. Just was wondering what other girls have experienced with their partner leaving.