She cries all the time for her dad.Help..............?

My daughter is two. She loves her dad. But because of his drug and alcohol problem we are not together and I have no plans for us to be either. She was a menopause baby. So I had her very late in life. Her oldest bro is 27yrs older then her. She wants her dad. She screams all the time for him. It has gotten out of control. I let her talk to him all the time. I also let him come for a weekend like every 3months. I just do not know what else to do. I sit with her and show her pictures of him and tell her he does love her. Does anyone have any suggestions.