This is for young guys who haven't experienced this yet. Your friends from high school and college will drift away.

One guy will move away.

Another guy will too absorbed in work.

That other guy will fall in with a different crowd.

Another guy will start drifting off by himself.

That guy will develop substance abuse problems and it will consume his life.

This guy will be married and no longer have times for you.

That guy will dump you and focus on his girlfriend.

By age 30, most or all will have drifted away. It's hard to find a person 30 or older who said they still hang out with most of their old friends from high school and college. Losing most of your friends from your youth happens to damn near everyone. So don't feel like something unnatural is happening. How you respond to it is what matters. Will you accept it and enjoy your status as a solitary male? Will you try to make new friends? Will you wallow in self-pity because you can't live life like you did when you were young? Will you spend all your effort trying to maintain your old friends even though they are more trouble than they are worth?

It's all up to you.