I started to feel really lonely lately, because I don't have friends and never really go outside besides the gym at night, so I thought about renting rooms to other people. Is that a good idea? I never lived with roommates, so I don't know what I should take care of and what is important. Are there any specific rules I should establish before doing it?
Do not, I repeat, DO NOT, do this to make friends. I advise most of my young coworkers not to move in with friends as it will quite likely destroy the friendship (not always, but usually).
Have you tried the usual advice for making friends (Hobby, community work, faith based, etc.)?
I just thought that being "forced" to be around someone could maybe develop a friendship between us, I'm not even using most of the space in my apartment, so I thought it would be a good idea. I tried usual stuff, but most of my hobbies are pretty obscure and I was just extremely awkward while doing community work, so I stopped. And online friends never worked out for me either.
the best case scenario with roomates isnt friendship, its basically ambivilance. you will completely ignore each other at best. at worst you will hate their guts, they will destroy your place and make your life miserable. the second case is extremely common. becoming actual friends is so rare its barely even on the table. that only happens in college.
It sounds like what your major issue is is social skills. Forcing someone to be around you in this state would be a very bad plan. Do you have consistent interaction with anyone (Coworkers, family, etc.)? You need to slowly start working on building your social skills (Remember, even in RPG's, getting along with people well is quite often tied with a skill or trait).
I do art commissions from home, so I don't interact with other people at all because of work and I cut contact with my family because of reasons. I don't know where I could find people to interact with.
How do you make new hobbies? I feel like I'm already into too much stuff, I barely have time for some things.
if you dont have enough time you stop doing other stuff. you make a new hobby by thinking about things you'd like to try and then doing them. it might not be exactly what you want to do but doing exactly what you want to do is what lead you to this isolation and you need to change it.
You sound pretty similar to me (Artsy, shitty family situation). I still socially network slowly and that is with a great deal of practice and effort. If you want, I'll be your first practice friend.