Trying to let him go

Hi! I'm a mum of a beautiful 11 month old girl.

Me and her dad split last year. 

He has moved on with another woman and I'm finding it so hard to let go. Some days I feel good and others I'm so low, especially when he comes to pick up our daughter. 

He cheated back when the baby was 4 months old, since then we were trying to sort out our relationship, for 6 months he dragged me along thinking we could be a happy family, he recently confessed he had no interest in it and was only around to make it easier to see the baby.

He told me he doesn't want to try any more, the day after he's dating someone else. 

Has anyone ever gone through anything similar? It would be nice to know I'm not alone.