Relationships take effort and luck. You have to work on yourself to be prepared, put a lot out of effort into social things to meet people and develop relationships, and then most don't work out and you're sad for a bit.

The luck part is a huge part of the equation. Two people are perfect on paper but the "spark" doesn't happen. Maybe they could have a great relationship but the starting conditions weren't right to form a relationship. Having a close relative die, or having a mental health issue really early in a relationship can force a wedge that can't be overcome yet. A normal wedge that all relationships deal with regularly once they're established, but can't deal with in the first few weeks.

The only advice that worked for me (I was raised with very few other kids my age) when I started dating in college was that the skills to make a romantic relationship were just people skills. That I should intentionally strike up conversations with anyone I don't know. Most people have something to occupy their time. I try to find that out in the first conversation I have with someone. You can see when someone's expression changes when the ice breaks and they shift into excitedly talking about a new personal best in a 10k run, or getting a major part in King Lear, or published their first full comic book or novella.

I had to hone my ability to talk about my hobbies. At the time I was finding gargantuan prime numbers. I had to work on how to describe it to people to make it slightly approachable.

I also figured out that a huge part of wanting to be in a relationship was family pressure. I had to be at a place where I wanted it, and not because aunts and uncles poked fun at any young single people in the family.