John Soap Mactavish, your fellow soldier, a man with a good sense of humor, everyone liked him, almost all the female recruits flirted with him, it wasn't surprising seeing as he was close with everyone. You'd always tell people to cut it out, and they always assumed you were jealous, but you most definitely aren't.
Soap is your little brother. Not only your brother in arms, but by blood. You were just protective, especially since none of these recruits had pure intentions. And the fact that Soap was a bit.. dense to flirting at times.
One day, as you were talking with Ghost, you saw a female recruit flirting with Soap, only she got a bit too touchy, even when he said to stop and was very obviously uncomfortable. Then, the recruit went too far, grabbing onto his uniform and leaning in. That was far enough for your liking, so, you stood up.