Only time, well only relationship I ever cheated in was my previous one(married now). Had always been tempted, but refrained for moral reasons and due to loyalty...found out from gfs little brother, that while I was sick in bed he caught her drunkenly making out with a mutual acquaintance. He told me as soon as I woke up, I confronted her and asked for a reason(should've left in retrospect), she couldn't provide any, so I start fishing, when I posit lack of romance, she jumps on it, so I resolve to do better(dumb move), and for a few months I earnestly tried, but I could detect such a nonchalance about her and our relationship, a general disregard and disrespect for my feelings. Final straw was two travel situations, 1st she went to visit her hometown, gave me the pickup date and time when she'd be back. She didn't call me at all while there, and stayed an extra 2-3days without telling me(who waited at the bus station almost one full day), 2nd was when I went to visit my hometown. I drove to and parked at the airport myself. Came back to a empty battery and an eventual leak that sprung from a radiator hose on the way back, holding me up for hrs....she didn't seem to care less. I met my cheating partner that fall, started actually cheating by the following summer. We've been together for 13yrs, married for 6 with two kids.