As a guy, where do I draw the line between making my advancement with a woman and being desperate/creep?

Ok well then find someone else or have a fucking decent conversation to her about what's up.

Get to know the girl as a person first, and you will better be able to read her attitude toward you

Reject your humanity and embrace your inner demons. Fall in love with yourself. Break the wall of reality as you transcend god itself.

Honestly, the difference between making an advancement and being desperate/creepy depends on your ability to accept rejection.

If you invite a girl you've talked to casually before to go take a coffee or any other activity, it's not creepy. If she accepts, hooray, else, accept it and continue with your life. It's her loss, right?

The creepy ones are the ones who can't take no for an answer.

It is so much harder to stomach rejection when you feel out of other options though. I wish more people understood that. I've been effectively friendzoned by a girl recently because I read into her interest way too late, and it feels like the world crumbled around me. There's no other girl on the horizon that I feel I could connect with on a similar level and it makes me anxious and frustrated.

>Being an ass burger is almost certainly never attractive

Don't confuse meme autism and neckbeard memes with real life aspergers. If anything, high functioning aspies are usually very good looking and will look much younger than most people due to their expressionless faces that don't wrinkle.

That's why you have to "advance" with your relationship in a transparent-ish way. Planning activities with just the both of you is a pretty explicit way to demonstrate that you are dating (unless both talked about it beforehand, or have been good friends for way too long, and you both rejected the idea that you could be dating).
If things go well, then you can talk to them about going further and becoming exclusive.
Some girls will take advantage of some guys, flirt with them, go on dates with them, but will refuse to acknowledge their relationship with you. Those people are pretty toxic and not girlfriend materials.

Did you read the rest of my post? Nobody but the most superficial thot cares about the amount of wrinkles on your face. But they do care about you being clingy and anxious nerd that takes everything too seriously and that shit stays with you even if you'd look like fucking Brad Pitt.

If only the rejections were actual "no thank you" rejections, but instead they're wishy washy "I'll think about it" white lie rejections that will confuse the shit out of men. Why would guys give up if they believe "maybe" literally means maybe? Literal interpretation of "maybe" means that there is a chance, and sometimes men will actually take that chance and keep trying. Men get told all the time to be more confident, assertive, and keep trying, so of course they will keep trying and being invested.
In some cultures it's actually considered polite to reject the first offer, and accepting the offer when asked again. This is to avoid seeming too cheap or easy. It's more commonly known as "playing hard to get". And I'm not talking about pestering women until they scream and threaten to call the police. I'm talking about treating women like people and not putting them on pedestal. If a woman says "maybe later", I might actually ask again later if I already know her and think she's cool. She's a person just like me and we both speak the same language, there is no reason why she shouldn't give me the same level of respect.

To be clear here, I'm only talking about verbal communication. Touching anyone without consent is wrong, there is little to no room for misunderstandings there. I'm talking about how shitty it is to reject guys without actually rejecting them, and then hoping they will read your thoughts instead of your words. You can reject men by being direct and polite, and most men will take the rejection when there is no room for other interpretations. I understand there are men who keep trying even after that, but that's a whole other thing.

The way it was was that she first started flirting with me while she was pretend-dating my friend (they weren't together anymore but because of reasons they decided to hide the fact). Out of respect for my friend, I've rejected, but I kept in touch with her because she had a lot of unresolved psychological shit and helping her made me feel like I'm doing a good thing. We went out for coffee a few times and she called those times "dates" and it became more and more obvious that she's into me. However I was still kind of unsure since her moods kept ping-ponging all the time and she was really hard to predict about what she really wants from me (sex? serious relationship? fwb?) and I had a lot of my own shit to solve anyway. She didn't want a fwb. Eventually she grew on me and started falling for her, so I was looking for a place to rent for us together. One day she sobbed on my shoulder about how she can't get a bf and was bullied in school and has a chronic illness and shit. Like a week later she fucks some guy from Tinder and she messages me about how she ravenously ripped her clothes away with him and did the nasty.

So yeah. I feel like my feelings were played with, cheated and made fun of. It's not even for the lack of trying - I was trying to be initiative but not overbearing, and in the last week I've called her out like three times.