What's happening to my relationship?

So my boyfriend was at bootcamp for two weeks and now he's home.. he wrote me all the time & said he loved/missed me & all, but now that he's home everything is different.. he doesn't act the same.. he acts like a jerk at times & just acts like i'm something he can't get rid of.. he still says he loves me but i don't think he means it.. he used to say he'd be with me forever and now he's just saying till we finish highschool.. he's 15 btw. Idk what happened though.. everything used to be so perfect, and now i barely know him at all..