If you are even for two seconds remotely considering telling ANYONE, let alone your father how you feel about an ongoing situation especially one like this which involves a parent (one of the two most pivotal human beings in your life), please do.

I have a rough relationship with my dad as I got older too. Same situation. Parents divorced, Dad moved on, the girlfriend isn't the greatest but my situation was different because my Dad cheated on my mom with her as well.

I told my father how I felt about it one night because it all bottled up so quickly and the response that he stated did lead to me cutting him completely out of my life for the last year. Recently, he reached out in attempt to rekindle things, but my father was never a great person like your dad seems to have once been.

I am only 23, but life is so short, and you never know how your Dad might be feeling. I am not a parent yet, but I can imagine that your child is always and forever going to be someone who you would do absolutely anything for and love more uniquely than any other relationship. Maybe he is embarrassed? Maybe he knows what is happening is wrong, but doesn't know how to approach you? Men are different than women are in general and especially when they feel they are failing as a man (in this case, as a father).

I strongly suggest getting together and telling him how you feel, as raw as possible, and getting it off your chest. In my opinion, I feel like that's the only way that you will ever be able to begin to rekindle the relationship and figure out a way to get your old Dad back.