Can I legally still see my ex boyfriends daughter?

My ex boyfriend and I just broke up after being together for 4 years, Last month. We have no plans on getting back together and the breakup was a very messy one. He, and another girl he was previously with split up in 2011, which was her decision. However, she was pregnant with his baby and didn't know until after the breakup and he got with me in 2012. The mother didn't want anything to do with the baby after she was born and pretty much neglected the baby at all costs and refused to come pick her up and got involved with drugs. My ex has had full custody of the baby ever since she was dropped off at his house when she was a couple weeks old and he went to court. My ex wanted me to breastfeed the baby since she was so young and he knows its really healthy for her. I went to a lactation counselor and got hormone pills to start my milk flow and breastfed her on and off for about a year and a half. My ex had a job as a travel agent but quit I after a while to be with me and his daughter. His daughter even started calling me mommy when she was around 11 months, which melted my boyfriends heart. My boyfriends mother was also around to help out with the baby. The baby loves her dad and always wants him and seems attached to him when at home. If out in public, she would throw a fit unless it was either me or him holding her. The daughter is turning 4 this year and I feel like I have always been there for her and are a significant part of her life but her dad won't let me see her. I always spoiled her and played with her. I have a younger sister who is 13 years old who always played with her too. I always took that little girl out to do mother/daughter/aunt (my sister) things. It really upsets me because my boyfriend is an only child, doesn't have a father and only has his mother to take care of her. When we were together she could be with all of us including my family. Can I still see her? I really miss her. How do I get over this?
Can I legally still see my ex boyfriends daughter?
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