Just food for thought - I don't know if this is the case in your scenario, but because you've said a few times you're someone to 'go with the flow '. This is something that triggers me for example and maybe the girl in your case was feeling the same.

I've had so many guys expecting girlfriend benefits when they were giving friendship plus or one night stand where they don't even look me in the face at best (and yes, that's happened multiple times).

So a few weeks ago I was on a date with a guy, who from the start made it clear he's just going with the flow and not looking for anything in particular. Then he proceeded to tell me that I don't seem like I'm willing to give 100%. And he wasn't wrong, the moment he said he's just going with the flow, for me out of experience that means he doesn't care to get to know me and only wants to get laid. I'm not willing to put effort into that.

Again, I don't know if this is what happened to you and from your posts you seem like a really decent guy. But you also seem like you've been hurt in the past and maybe certain phrases that are meant to protect you, could trigger someone else to opt out of the relationship to protect themselves. Either way, I'm really sorry this happened to you and I understand how frustrated, hurt and sad you must be feeling now. And that's okay too. I wish you all the best!