My heart goes out to you. I have lost many people I have loved, but over a period of 60 years, not 21. You will never forget these experiences, but you will eventually heal. Your friends will always live in your heart.
As you say, losing those you love does make you aware of how important it is to be there for those in your life. But if one of your friends you have been there for does still choose to end his life, it’s not your fault. Our best friend chose to end his life 15 years ago. It was devastating. He came to say goodbye on his way home from work that night, but we didn’t know that was the purpose of his dropping in. We were the last ones he spoke to and our time together had been good except that he seemed to be in a trance and crying for part of it. He was extremely sleep deprived because of what was probably an undiagnosed brain tumor he didn’t mention. We only knew he was hearing voices and found it hard to sleep.
The evening ended with hugs all around, and he refused our offer to drive him home. He said he’d be fine and even called to let us know he got home safely. That night he shot himself. We went through all the “if only” scenarios and whys with each other. If we had only said or done this or that maybe he would have changed his mind. But in the end, it was a decision he made and he had a very strong will. He didn’t tell us because he knew we’d try to change his mind. But he still wanted to see us once more because he knew we did love him and he loved us. I suppose we will always wonder if anything we might have done differently would have brought about a different ending, but after all is said and done, God let him come home.