How can you get your boyfriend back if you have a 7-month-old baby together but he is dating someone else now?

You can't do anything. It's his choice and his alone to determine who he wants to be with and how he wants to live his life. That's why it's generally a good idea to plan ahead, know who you want to spend you life with and commemorate with with marriage before bringing a child into the world. Really sorry to hear about this hon, but it happens. Be sure you get the father of your child to pay Child Support. He should be taking on the responsibilities of a father no matter who he is dating or living with. Good luck