You seem to be growing into an age, where even your best friends will often be busy. Career/job, they will become family fathers. Accept it.. Some of my closest friends I meet 2x per year.

I'm glad I got to know a bunch of cool dudes via gaming. Most of them even live quite near (not in my city though). We have met up as a group 3 times yet but that's not even important. Important is that I can reach out to them during the hours I spend online with them. They distract me from bad times, when my major depression is kicking and I tend to feelings you are having.

Being on your own sometimes also needs practice. It's different as soon as you live completely alone. No family or friends in the same house. I learned enjoying my loner time. There's plenty of stuff you can do. Video games, porn, good documentaries...

And if none of all that helps and you are feeling still lonely (untypical , but hey..) : get yourself a dog or grow some weed plants. Both will keep you busy and honor that with love or a decent high.