Written by someone with little understanding of the requisite material
The requisite material for the topic at hand is "dating a person who clearly thought there are implied social contracts at play, and attempting to make it work out anyway"
OP is asking about "How do I fit into society?" not "How should society function?"
I agree with you that a lot of implied social contracts are bullshit. But also they exist. Until you have had that talk together to figure out the relationship, there has to be some assumptions. People don't always have deep "what is this relationship" 2 minutes into the first date. Assumptions are not always bad.
Your stance is that the assumption is "I have no obligations until I've agreed to them." This is itself merely an assumption to make and not just "fact" of some sort. The vast majority of society has the assumption of "The relationship IS an obligation to some degree based on context." I'm not saying which assumption is "right," I'm just saying how it works for most people.
If I'm in a relationship where I'm committed enough to refer to the other person as "my partner" then I'm going to err on the side of not hurting them, regardless of who is to blame. If I can prevent the other person from being hurt just by working along with their assumptions until we can have a conversation where we make things explicit and there are no more assumptions, then why wouldn't I do that, unless "being right" is more important than my partner.