"Amassed a large collection of nighties"--that made me laugh. I pictured underwear hanging on the wall like pieces of art, a little light over each one and a little plate below with the name of the piece, what it's made of, and who gave it to you.
Wear what you want. I don't see the problem even wearing the ones your ex gave you, but if it makes you feel funny, don't wear them. I see the emotional value of tossing those.
Guys don't care. We don't think about who gave you which nightie; we're just glad you're in it. I would be wary of a guy who cares too much about where you got your underwear.
Thanks for the question.