Boyfriend thinks I'll cheat???

My boyfriend always says "girlfriends always end up cheating on there boyfriend if he's in the army" and it honestly upsets me so much because I could never and would never do that. Then I start getting upset because I feel like he thinks I would and I'm not like that. I'm so madly inlove with this man and want to spend the rest of my life with him.

Why does he have to go and make such stupid comments like that.