You saw the bad moon rising, and it was not your imagination. One of you had hot pants and a wandering eye, and vows may have been broken. Was there a not-so-ex ex in the picture?
If so, it could have proven to be a distraction. The tempted-to-stray partner was distracted, distant; the other felt sad, desperate, terribly insecure. At times the suspicion got so bad that spying was indulged in. Pawing through a lover's pockets was tacky, but that was the least of it. This relationship may never have gotten secure and content. There was an undercurrent of friction and too much awareness of other options besides sticking in this relationship. Nonetheless, there was a lot to recommend staying together. You shared a lusty physical connection, similar senses of humor, a love of play and fun. All of that could have gone a long way, if the jealousy of one partner didn't sour all the good times. If you were the green-eyed one, here's a piece of advice for the future: Nothing makes you less sexy than demanding and pouting and blustering; something to keep in mind for next time. If you'd tried playing it a little cooler your lover might have just come hither.