Thanks for all your help Otter.
So far I've come up with a strict guideline:
1. If something makes me uncomfortable, I don't do it.
2. If I'm not sure if something will make me uncomfortable, I don't do it.
3. If I do end up doing it and am comfortable with it, that doesn't green light every other thing I might be uncomfortable about.
4. If I do end up doing it and am uncomfortable with it, that doesn't mean I'm now stuck having to forever accept it.
5. Remember: boundaries are flexible and can change.
6. Always communicate how I feel towards others and don't feel bad if they seem upset. I can be polite and nice, but that's not the same as letting them walk over me.
I've written it down like that. I don't have an idea of what my exact boundaries are going to look like and how headstrong I'll be, but at least it's something I can try and work with.
As for N, I've decided to message her in about two days from now because it'll be her birthday and I'd feel horrid if I didn't say anything then. From there on I've read it's best to not start with talking but rather do something together like gaming, so that's what I'll propose. Hopefully she's done some soul searching too and I can have an actual friend this time around.
~ Grey