DEAR ABBY: When I was 16 and my sister "Daisy" was 18, I found out she was in a sexual relationship with my boyfriend, "Tyler" (also 18). I broke it off. She then asked if I minded her dating him. I'm sure I said I didn't, but I thought, "Why ask? You were already having sex with him." (He and I hadn't.) Tyler and I remained friends through the years. He was my first love.