Why do *some* men get offended when a woman offers to pay?

I'm all for equality, I always try to pay my half -I insist especially when I'm not sure I'd like a second date- but men don't seem to like it. Even my boyfriend didn't want me to take him on vacation. I had been asking him for a year and a half. He wouldn't let me pay and he didn't have enough for a trip. The second summer I asked him I got mad at him "so, you wouldn't take me on vacation if I couldn't afford it?" and he said "no, of course I would and I wouldn't take a no for an answer" so I asked "what's the difference?" and now I ask you people the same.
Do you let your date/partner pay if he or she wants to?
Why do *some* men get offended when a woman offers to pay?
Why do *some* men get offended when a woman offers to pay?
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