Don't know what to do...

My daughter will be coming up on 6 yrs old. Her father has seen her maybe a total of 6 months in 5 years. He has been in and out of jail and has used drugs almost the entire 8 yrs I've known him. He'll go a year without seeing her then pops up out of no where. I thought it was ok when she was really little to see him because she didn't even refer to him as daddy until about a year ago. The times he has seen her I've always been there, she was never alone with him. But now, she's constantly asking to see her dad. He's supposedly clean now after receiving a 3 yr probation sentence but I told him no he couldn't see her when he asked. This was the first time he's asked for her since birth. He's never paid a dime and has never called on bdays or holidays. I don't know what I'm suppose to do. I want to shelter her from the truth about him and I never speak badly of him around her but I also want her to make the choice for herself if she wants him around or not but don't think she's old enough to make that choice. She refers to my bf as daddy but knows he's not HER daddy. I'm at a crossroads here and don't want her to resent me later down the road for not allowing her to see him. My bf despises her father because of his inconsistency in her life and because he's a POS. What do I do?