Baby's Last name

Hey everyone. I'm sort of in a really bad situation right now deciding who's last name my baby will carry on. I have a son that is 6 years old that has his fathers last name and mine. This time around I'm having a baby with a different guy and don't want the baby to carry his last name. Simply because I've learned that with my first son I gave him his fathers last name and he didn't stick around. An other reason why I feel like I don't want to give him my fiancé's last name is because I don't want my kids to feel like they have different last name. So as of right now I'm sticking to having my last name first and then my fiancé's.