HOW DO YOU BREAK UP WITH SOMEONE

I recently got in contact with my first love, we've been seeing eachother on weekends for the past couple of months and I have fallen in love with him all over again. I do currently have a boyfriend, who I'm living with and I know I want to be with the other. I just don't know how to tell him, he loves me like crazy but I know I have to do what's best for me. I picture a better future with my first love, he already wants to buy a house with me and start a family, where my current boyfriend is too busy spending money he doesn't have and partying. I just don't know what to say. Please help.

EDIT: I had my boyfriends permission to hangout with the other guy

UPDATE: I broke up with him and now am happily living with my first love. Everything is just how I imagined❤️