What have I done?

The drinking didn't stop, it followed day after day and I fell into a never ending haze that would lead me down a road I never meant to take.
Last week...two days after the funeral, I found myself at yet another party. No familiar faces...except one. Marcia had invited me over that afternoon and being drunk off my ass I said yes without even considering my options. I didn't expect it to turn into anything, but man was I wrong. I can't even remember who leaned in first, all I know is that we ended up doing it on the living room couch. I tried to leave in a hurry without being rude, but I instantly felt the regret...and the hurt that Kit was sure to feel. I didn't tell her right away, and so then she heard it from someone else. I'm guessing Marcia spread it around town that we hooked up, a greaser and a soc... and me engaged. I went home and drifted into my usual sulking spot on the bed until I heard Kitty come in the front door. I stood up, but she was in the bedroom faster than I could even find my words to start,
"I heard about you and Marcia." she said.
I felt the world weighing down on me. I was ashamed and so, so sorry.
"I'm sorry Kitty...I reall..." she cut me off,
"Its okay, I forgive you." She said.
It was almost too easy, I didn't quite understand, but that didn't interfere with what we did next. It didn't make me feel any better considering that I had just done it with someone else only hours before, and Kitty's response didn't make me feel like I was exactly off the hook. My mind was spinning, and I couldn't grasp the concept of who I was anymore. I'm not the cheating type, it's just not me and I don't tolerate that at all, but now I'm a cheater, something I used to look down upon, and people always tell me.... cheaters never prosper.