J.C.
Its time to grow up. (please don't take that wrong). You are an adult, you are a mother, you need to act like one. Take your daughter and go to your mom's house for a visit. Tell her everything that's going on and listen to her suggestions. If its possible, move out of your boyfriend's mother's house immediately. Pack up, take your daughter without a scene and go back home with your mother. Ask your mother to come pick up your daughter so she's not there when you're packing and doesn't become a point of contention.
You need to get out of that house, start your life as an adult. You can't control what your boyfriend is going to do, but you can't let your life pass you by while you sit under the thumb of a controlling boy and his controlling mother. He MAY decide to petition for custody, but he won't win. He will end up with partial custody.