Do i have to file taxes with my bf if we live together?

We have a 2 year old and a 8 month old. Last year he filed taxes and he claimed our daughter. Our son was a newborn and he couldnt him. I worked but but not alot so i didnt get a return we had filed seperate but also because i didnt live with him. This time we moved in together and we can claim our son. My mom said we HAD to file it jointly because we live together but i was hoping i can do it seperate and claim DD and DS. I worked more then my bf and honestly i dont think he even made enough to file (he has been on and off his job). Is it possible to file on my own? We arent married and i dont know the rules 100% i know im asking so early but i want to get an idea because i need to work full time for the rest of year to be able to file if not ill probably lose the chance to get a refund. Sorry if this confused anyone.