Thanks for all the replies.
I believe there is also a biological trigger at play.
For instance, there were periods of my life when 8 women out of 10 would be datable/fuckable in my eyes.
This month it's more around 1 woman out of 100
Also, interestingly, a month ago, after I skipped a night of sleep for some reason, I was extremely tired the next day but at the same time I was having this weird urge of having sex with just any woman. I'm pretty sure I wasn't functional at all down there due to extreme tiredness but my brain kept screaming at me "FUCK HER" upon any random girl's close encounter. This was quite an experience.
So, mildly depressive state, diet, sleeping pattern, stress, etc. also play a big role I believe.
Then there is also the "why bother again" state of mind when you have enough experience to know that a new partner will equal having new problems since most women bring their luggage full of negative past experiences that they can't forget/forgive, craziness sometimes, lack of financial independance, etc...
Breaking up very 1 or 2 years can become tiresome even for someone like me who does not want to marry or have kids EVER.
Anyway, after a few months you get tired of being alone and then you start to think that you don't care about the problems a new partner will bring in your life.
The weird cicle of sex/life I guess.