I would never ever permanently remove a piercing for a partner. or anyone else, and the only reason I would temporarily remove one would be if it was causing them or me actual pain during sexytimes (or I had to for an operation for example).
To me this is equally as important as never getting a piercing for a partner, too.
The only person you should ever get or retire a piercing for is yourself.
Three things you should focus on here are:
1) You got them pierced for you. Partners will come and go, but you will be around you forever. So do what makes you happy :)
2) It sounds like you have a lot more self-love with your piercings in. Don't ever do anything for anyone else which could lead you to loving yourself less. It's never worth it.
2) He's an EX and probably for good reason. Stop worrying about what he thinks. His opinions can stay where he is: the past.
Oh and as for it being a deal breaker: I would absolutely end a relationship with someone who said that my nipple piercings (or a different modification) was a deal breaker for them.
Anyone who puts that much importance on my jewellery / body mods is not putting enough importance on my personality and soul, and that is the kind of person that I don't I want to get to know at all, let alone be in a relationship with.
What the heck has a piece of metal in my body got to do with what sort of spouse I make? Nowt. I've experienced this situation from both sides. Some guys I've been with try to get me to remove or hide my mods, where others are clearly with be because of my tattoos and piercings because they think it's "cool" or something. Both are absolutely infuriating and hurtful.
I want someone to be with me for ME and the guys who last are the ones who see through my physical attributes, natural or paid for, and love me for my personality. The physical attributes should be an "extra": and feel like either a 'cherry on top' or 'a minor thing they can look past'.
Hope that helps!