Broadly speaking:
Some break-ups happen because you're young and inexperienced. Both parties are still figuring things out. That's okay.
Some break-ups happen because one or both parties didn't put in the effort they should have, or wouldn't -- because they were selfish, arrogant, didn't value the relationship, or were dishonest with their partner or with themselves as to their needs and motives which isn't the same thing.
Many break-ups happen due to unmet expectations. Were they fair and realistic? Was it just bad timing?
Sometimes people just don't grow in the same directions or at the same rate. While this may be painful it's also just reality and it's up to us to grapple with it. Nobody owns anyone and tomorrow's always provisional.
Other break-ups happen because one or both parties is dysfunctional in some way and those dysfunctional patterns --
independent of whomever you're with -- will play out repeatedly. Co-dependence is a big one.
Again ... broadly speaking.
Only time, introspection, experience and honesty with one's self and a drive for self-improvement will reveal to you the truth of what happened in any given scenario. We're all good at deluding ourselves. We don't grow until we stop that -- the process is often drawn out and usually non-linear.
No woman is going to make your life better, that's up to you.
No one will show up for you unless you show up for yourself.
Sometimes that means owning up to your failings and working on them, or it may mean going to therapy because you're unable to be objective. Or maybe it just means being an adult and taking care of your business so that you're not a walking disaster. No one can be perfect but everyone is responsible for harm reduction and risk management in their own life.
I've had good, caring relationships that simply ran their course, disastrous relationships with malicious and possibly mentally ill women, relationships that changed seemingly overnight but actually changed over the course of five years without me noticing. I've been an insensitive, arrogant dick to women that didn't deserve it, because I didn't know better and didn't pay close enough attention, I've also been lied to, cheated on once that I know of. There are women who have apologized to me, there are women I definitely owe an apology to.
Sometimes you're the bad guy, sometimes they are. Sometimes you're both just blithering idiots, other times you just wind up wanting different things.
Also, being 'in love' is not the same thing as loving somebody long term. Veeerrry different.
Women are just people. Delicious people that smell great (speaking as a heteronormative male) but they're just people like you, and learning to empathize with that and engage with that isn't easy for all of us, due in no small part to thinking with other body parts as we're prone to do.
@Captain Clown: it all gets easier with time, and eventually the context for your memories will change, and you will change, and you'll be with someone else and it'll be a better relationship if you do the required reading for the one that just ended. And there's no timeline on that. It happens when you're ready for it and there's no end point, just process.
Out of all the women I've been with there's only one I
completely regret, but I suppose she taught me what to run like hell from because that'll never happen again.