Whats wrong with having sex? its two people getting together and having fun... and yea maybe you couldnt think straight bc you were depressed, but AT THE TIME it seemed right and AT THE TIME it was okay, and the only reason why your worried now is bc your over thinking it and your thinking differently than the way you used to.
You grow, and as you grow you see things differently! dont put pressure on yourself!
what matters is now not yesterday... and plus, you can say you have more experience and thus! you are better in bed ;)
ps sluts are girls who sell themselves and dress (in fact hardly dress) and im assuming since you were so offended you are not like that...
STAY WELL! were only human =)