I split up with DD's father 8 years ago when she was a few months old. I stuck the relationship out as long as I could, although I was unhappy and didn't love him. It turned quite ugly after about six months of us trying to work out a civil arrangement of him still seeing DD. He moved back home with his parents over 200 miles away. This reduced him to seeing DD every 3 or 4 months apart (or when his parents forced him, and drove him down because a) he can't drive, and b) he can't afford the train or even the megabus 
). Also at the time, he did not have parental responsibility as we were never married and this was before the rule came in that fathers got automatic PR.
So eight years on, ex still lives at home with parents, is jobless and can't even be bothered to call or email his DD. His parents and sister keep in regular contact with me, whether by phone or email, as they like to know what DD is up to and really miss her. All of us have tried to drill it into ex's head that he needs to make more effort with DD, who currently does not want him visiting her on his own, but only with his parents and sister. She does stay at his parents for a weekend over the summer holidays and this year they're taking her away, which I'm only happy with due to his family also going, and who have promised they will not leave DD alone with ex.
The odd time DD says she really misses him. I tell her I understand that because I've been through that myself. My dad left when I was little and I rarely saw him, so I sometimes talk about my experience and feelings on that, so she knows she's not alone. I also tell her how much me and DP love her and make sure she knows that.
I'm not really looking for advice, but more of a way to vent, because I know there's nothing that can be done with the situation. Me and his family have done everything we can to try and improve his interactions with DD, but if anything, it just seems to be getting worse. I really wish he wasn't her dad. I wish she had a good one like DP.