Why did I involve myself with my daughter's dad when I know he was my downfall the whole time?

I know for me I had to realize I subjected myself to toxic relationships because I did not realize my worth. Once I started to see myself through the lens of God and whom He intended me to be toxic relationships started to diminish. In some instances I would realize later that some of those toxic relationships ended without me putting in effort into it. During the process of asking God to make me over I asked Him to remove people and things out of my life that would not bring Him glory and He answered. I would advise you to practice that prayer and when God releases you out of the relationship don’t cancel out the blessing by trying to hold on to it. You can have a productive co-parenting relationship without going deeper. The children will be blessed in the end.