Hmm .. well I've been married for 5 years but I remember my breakup with the last long-term girlfriend before that, when I lived in Japan. She was an absolute fox and batshit crazy in bed - far more than the other Japanese girls I'd known. We both liked drinking alot so we'd meet up, go to an izakaya, get plastered, and then have drunken 'anything goes' sex at karaoke/in an alleyway/at my place, until we were too tired to continue. Unfortunately - that's all we had. We were a perfect sexual match, but emotionally and intellectually nothing alike. We tried to make it work, but I guess in then end the sex wasn't enough to stay together.
Annnnyway, one Sunday she messaged me saying that she didn't think we were going anywhere as a couple. I replied promptly saying 'yeah, looks like it'. We agreed to hook up the next day (in daylight, in public, and without alcohol - we both knew if it was night time and we were drunk we'd end up shagging again) and finalise things, which we did amicably, and I haven't seen or spoken to her since. Last I heard she'd moved to Okinawa and was dating a US soldier. I guess once she got a taste for gaijin, she got it bad.
I hold no ill-will towards her, and I presume she's likewise - there was nothing particularly negative in our relationship. We had fun when we were together but fun alone ain't enough to keep a relationship going. On a positive note, 2 hours after we broke up I was on my way to a party and saw one of my mates with his girlfriend and some other girl going to the same party. I said to him "I've just broken up with the girlie. Know any single gals?"
I've been with the girl who was on the way to the party for 9 years now, married in 2006, and had a baby boy in 2008.
EDIT: And btw, OP, you sound like Ted Mosby.