Not saying yes to someone who asked me out. I did have a partner at the time, but I was literally in middle school, and it didn't last. While he and I (the guy who asked me out, not my partner) remained friends, I've started to develop a crush on him, and while I did have feelings for him back then, I ignored them as I felt I should stick with my current relationship, and I wish I hadn't done that. It wouldn't have lasted in all likelyhood, considering that we were, again, in middle school, but I like him now and can't really ask him out because of that.
