How to determine appropriate closeness?

I just lost 2 completely unrelated friends that didn’t know each other side were at opposite ends of the friend spectrum.

One guy lived in my complex and is a really cool super intelligent guy. I would hang out with him on occasion to talk about random stuff. He worked long hours in a toxic work environment and wasn’t happy in his relationship. So I gave him some distance and just dropped by every couple months. I’d see him around sometimes so it wasn’t like we weren’t in contact in between visits. He never actually went out of his way to visit me at my place so I just figured he was doing his own thing. Turns out he moved a month ago and I only just found out. He didn’t even say good bye to me.

The second was very close. He was like family. We shared a hobby and it was deeply enriching. I learned quite a bit and despite being a lot of physical work and gas to drive out there I never regretted the time spent. The last couple times I saw him he and his wife were stressed about things I made a point not to ask about. I suspect money was a factor, and with his hobby I am directly associated with that expense. He aburptly cut me off completely without warning or even an argument. And it really hurt when I realized it was over.

It seems I need to find middle ground in my relationships. Either I’m all in and fully invested, or I’m distant to a point of reclusive. My question is how do I create a reasonable distance while remaining close enough to still actually be friends? The first guy didn’t even know I thought of him as a friend.