Would it help explain the PUA thing if I tell you that one of the things I need to work on is not being too concerned for guys' feelings if I turn them down?

It does, and to be honest that (with girls' substituted) is still not a strength of mine either. I do it because I must, for my sake and theirs (if I couldn't say 'no' then I clearly couldn't say 'yes' to monogamy or even bigamy!) But it takes effort.

The ironic thing is that PUA tactics are optimised for girls with strong boundaries in that area. That is, most of the techniques suggested are ones for dealing with the fact that attractive, highly socialised girls are habitually biased towards rejecting rather than reverse. (Even so, I can understand your wariness.)