Should my boyfriend discipline my kids?

 
All situations are different and individual, and there is gray area, however my gut says no.
The most important thing is that your kids feel like they are your priority above all. The second the boyfriend, someone who isn’t officially in the family and who doesn’t officially have a parental role, takes precedence over them, it becomes a problem and it creates a conflict.
So it’s beautiful if your boyfriend cares, if he wants to be supportive, and wants to help you learn how to interact with your kids in a different way, but he shouldn’t be the one doing it. It’s up to you to be the one interacting with your kids, and helping set the boundaries and the guidelines for how things are going to be in your home.