Hello there!
I'm not the kind of guy who tells people to see the glass half full, but please, see the glass half full. The fact that some people suddenly just left you with no reason or explanation, it probably means they were fake friends, or simply they were there for their own ends, their own benefits, forgetting the beauty of true friendship. I know how frustrating it is, because everyone in my life has left me because I was brooding the whole time, but at the same time I was the most loving and caring, giving the best I can to sustain a friendship. But, I did lose all hope, until I met a few friends, two friends, actually, who are exactly like me. I have searched for people like them ever since elementary. Not really, but you get the point

And I know that seeing how immature people can get these days is indeed annoying and very mysterious, but that is a positive for you, because you are actually more mature than them.
And, never apologize for rambling here! I do it all the time

Please, keep having faith in people, because it will pay off one day!
Good luck achieving your goals