If making friends in our teens and 20s was so easy then we wouldn't need to make more friends in our 30s.
Making friends isn't the hard part. Maintaining the friendship is. It's a lot of effort and often involves doing more work than the other party, especially if they have a busier life. But it also involves a lot of failures, as plenty of them just aren't meant to be. I look more at the effort others put back into the relationship than how much I like them, as the former is a much better indicator of the potentials.