<human>: Can you provide a brief rundown of the text in within 3 sentences?

Some back story on my affair, if anyone cares. No need to berate me, I already know I am a terrible person. Obviously using a throwaway.

I was on and off with this girl, lets call her Sam, for about 3 years through late high school/early college. Timing was just never right, we were immature kids, ect, ect.  She was the only one of my exes I kept going back to though. We just could never stay away from each other.

When I transferred to a new college I met a someone, lets call her Mary, and we have been together ever since (around 5 years). Have several pets together and are saving for a house. Mary started dating someone and for a while neither one of us contacted the other one for nearly 2 years of Mary and mine's relationship, up until about 6 months ago.

I got contacted out of the blue by Sam when her girlfriend had broken up with her while she was in Basic for the Army. She just needed a friend. Once just talking turned into us seeing each other again, the trouble started. Those damned feelings came about.

Recently while I was visiting my parents, I saw her and next thing I know we are going for it. I know exactly what I am doing, and do it anyways. 

When I got home to Mary, a feeling of guilt washed over me, and somehow I ended up initiating really passionate sex. Our sex life was rather lack luster and actually has caused a lot of relationship issues in the past, so this was something way out of the norm. It keeps happening though.
<bot>: I fucked my ex while I was home recently, feel guilty, trying to cover the guilt with hot sex with current partner