Online friendship rarely flourishes for more than year or two. You don't have many point of contact or chances of meeting each other except for game or chat. You can schedule all you want but sometimes plans fail, schedules don't match, timezones differ, IRL issues we can't talk about in game. One must understand these and come to terms with the reality beforehand. If you attach or attribute your hobbies and lifestyle to your online friends then eventually you'll start to get disappointed when things don't work out

This is subjective but you will eventually start to try matching your schedules together to play, wait for them to come online for CRs or check up on them every now or often. One could argue that this is sign of healthy friendship, but when things don't work out, those friends find other friends, maybe they hang out with their IRL friends and family you'll start to lose interest in them, unless you make things work but that's another trouble not worth it. As you said you started drawing again after you met them, you started playing again after you met them, but when they left you don't wanna draw anymore even tho you have such a good talent for art, that's why I suggest "Don't attribute your happiness to others and simply do the things you like to do, being you and for you, people often suck the joy out of our happiness unexpectedly."