I Don't Have Much of a Relationship With My Dad

I don't have much of a relationship today with my dad, but that's due to my mom. I moved out of state in 2003 to be with the love of my life. Since then, my parents have only come out to visit me once, when I got married in 2004. Meanwhile, I have been back three times, all for family functions, and at times when money was extremely tight. My parents, especially my mom, have hurt me and my wife over the years. This year, I wrote a letter to my mom, expressing that pain. I know my dad knows what I wrote is true, but he defended my mom, and told me I had to apologize. I did, in a card. He said I needed to apologize by calling and verbally saying it. Despite my asking that this be kept between us, my mom told my sister, who sent me a nasty letter. I do not speak to anyone in my immediate family right now, and I'm better off that way.