My 20 month old dd's father has never been in the picture. About 3 months ago I started dating. She loved this guy and played with him all the time. Now she acts like she hates him. I don't know what to do. He tries so hard and she just scream that she wants me. Any advice would be greatly appreciated.
Assuming that there was no rage or abuse directed at her from your boyfriend, your daughter has likely just realized that your boyfriend is a competitor of hers, fighting to see who gets Mommy's time and attention.
For now try reducing the time that the three of you spend together, and give your daughter more alone time. Then gradually reintroduce your boyfriend while still making it clear to your daughter that she is number 1 in your life (by holding her on your lap, telling the boyfriend how great she is, and so on). Let her see that he cannot be a threat to take you away from her. Remember that you are the only parent she's got, so she'll be very worried about losing you.
Dr. Mike Bradley