"Time heals everything" is essentially true. You'll eventually move on emotionally, and the people who actually matter in the long run will either remain good friends or be fond memories. The ones who don't, you might remember with a kind of regret that they weren't good matches for you, but you're better off without them anyhow.

There are a ton of people in the world who all have their own specialness, and you'll see that in someone else eventually, maybe in multiple other people throughout your life.

Not ruminating about it + time + having stuff to look forward to in life + paying attention to my present

Taking a step back and really looking at who they really are, how they really behave, not hiw I imagine them to be or intentions I assume they have.

Either because they turn out to be pretty bland people I have been able to bulid fantasies around or because our issues was actually just their bad behaviour that I was able to imagine excuses for, or because I realise that we are not a good match (we want different things or tend to trigger each other in unhealthy ways) and a relationship between us would be more hurt than it's worth.

Like you seeing her ableism and homophobia instead of just your fantasies around who she is and how your relationship would be.

It just sort of happens naturally after you process that realistically you wouldn’t have been compatible with who they really are in the first place anyway/it would’ve ended REALLY badly.

Maybe you still think about them from time to time, but it doesn’t hurt.

I learned to hate myself. Focusing on my constant failures has led me to forget most people over decades.

I never really fully stopped caring for them, but I don't want to build my life with them.

An unexpected side effect is that I felt exultant when they found someone to build their life with. I sleep better knowing they are cared for.

Anytime I look back and think "what if", I realize it would have been bad. We're both better off separate from each-other.

And it hurt to be near each-other, so we don't stay in close contact.

But none of that invaldiates all the wonderful things we know about each-other, better than most people do.

And it doesn't stop us from celebrating each-other's victories from a distance.

As others have said, time. Also, the realization and repeated internal reminders to yourself that they were not who you thought they were.

It's very easy to build up someone in your head to be better than they are and to fill in the gaps with positive assumptions, especially when you're crushing on them. You have to realize that those fuzzy feelings were in your head. The feelings weren't based off reality, and they obviously weren't the same feelings in that person's head. At the very least, those feelings weren't based off the full person, because you didn't know them fully.

The version of them you liked didn't exist, because that version wouldn't be (in this specific case) homophobic, ableist, hating special needs students, and making fun of you behind your back.

Yes, it may hurt to remind yourself of the reasoms they are shit, but it'll hurt less than allowing yourself to pine for a "what could have been" that was based off a version of them that only existed in your head.