If the person you love turning out to be a slut is a dealbreaker, you don't really love them at all!
What absolute garbage. How seriously a partner takes relationships and love is not only relevant, but extremely important.
This kind of claim is just an excuse by those who want to pretend they haven't trivialized the act of intimacy for themselves through mistakes, poor judgements, or .
Maybe some people can be told "You're the only one for me. Ignore the various other people I also promised were the only ones for me, this time I'm sure it will work out" and be satisfied, but those who aren't willing to accept that are completely justified in not doing so.
Maybe some people are fine being told that when they make love with their partner, it's in an emotional way that's different from when their partner has done it just for physical pleasure. Others will hold that since the act is no different, neither is the significance, and once the partner decides it can be meaningless then that's the end of it.