idk what it is with the men you've experienced but misinterpreting cues is one thing if there was no verbal statement otherwise but with the fact that you have made it clear he has no excuse. And it's not Men, it's MEN WITHOUT BRAINS clearly. A decent male friend would understand and respect your boundary, period and trust me, there are actually men that aren't so inept with women.

if he's a good friend you will be able to have a conversation with him about what flirtation he is referring to and clarify this behavior with him as not flirting or coming onto him. I fear that he's kind of thick in the head though as it sounds like you've already had to make it clear to him multiple times and it's not getting through.

To be honest he sounds like he's a lion lying in wait... "maybe if I stick around she'll change her mind" kind of thing and based on this delusion his interpretations of your friendliness are exaggerated by his false hopes. since his base is that he expects and hopes for you to change your mind about him, he's reading into things through that filter.

need to decide if this friendship is worth it if he doesn't give up on anything more than friendship