Would you be ok with your potential partner giving you an ultimatum on something you might be willing to change?

Let me give you an example.

Let's say you start dating someone new.

They find out that you flirt with others, just for fun, and not even in a serious way.

But Let's say this is a 100% deal breaker for them with no room for compromise.

Would you rather them

1. Just break things off with you?

Or

1. Let you know this is a big deal to them, and if you want to continue dating them, you need to stop this?

I'm asking because im in disagreement with a friend. They say option 2 is too controlling. I say it's better for the person to know a deal breaker as opposed to just leaving.