[MF] When my gf and I (M) swapped partners with her college (F)riend

Hi all, first time poster, long time lurker etc, etc. Writing always terrified me but thought I would give it a try.

My girlfriend Kallie has a friend, we can call her Maddy, who is the same age (23) as us and is in a long-time relationship with a high school sweetheart, Ryan. Maddy and I hit it off pretty well when we first met. Not sure if it was liquor or personality but we always had a really easy friendship and we get each other well. My issue is I end up developing feelings for my friends, even when I am in a relationship, and Maddy was no different. It is always out of the blue that I catch this and one day I suddenly found myself attracted to her. I started to catch myself checking her out from time to time. I started dwelling on her long dark brown hair, striking light blue eyes, pale skin with an early summer tan. Her full hips that give her a defined, pear-shaped ass. Her B-cup breasts which sit like two apples among the leaves behind her straight hair. I lusted for her, imagining every possible detail that may be underneath the clothes I could never take off of her.