Why would my guy friend look very nervous and flustered when I said “I don’t chase men I replace them.”?

Probably worried you'll order a new guy and replace him.
Because it's just another childish slogan people say about relationships that don't mean anything in itself as context on relationships change the result
Because that saying is so cringey and juvenile to say
Opinion
2Opinion
Because you sound like an idiot sorry but it's true
so you don’t think if something doesn’t work out you should move onto something else and replace them
I wouldn't say it likethat. and if was something good and worth fighting for id work on it before giving up
You'd have to ask him.
Superb Opinion