Not that I'm siding with your mom... or maybe I am ???
When I was 18, I had a GF (didn't figure out I was gay yet). I brought her to the house, and attempted to get my mom to allow her to spend nights there. My mother refused, and told me that if I wanted to do that, get a job, my own apartment, and then I can do anything I want to... which I did.
Sure... I had some resentment at the time, but she was right. At that age (and yours), there's NO (!!!) reason why she should still be supporting me (AND her). It's her house. If you want to live there, you have to abide by HER rules. If you want freedom to do whatever you want (or with whomever) you're going to have to leave the nest and do it.
IMO making out with someone in your mother's house is disrespectful to your mother, and to whomever you're making out with. You think you got it all worked out on how it's going to be on the outside, but honestly, you don't have a clue. Granted, SOME of the stuff you worry about is possible, but it's tip of the ice burg stuff you're stressing over.
You WILL make other friends, gay or otherwise, and you WILL (eventually) find someone... unless you're hell bent on sabotaging yourself for the rest of your life - and even then, there's still going to be people who like and care about you, in spite of yourself.