Forgiveness is the laying aside of judgement. The tragedy here is your loyal defense of your mom precluded you from sharing a loving life with your Dad AND his true love. All she did was love him, and likely she would have loved you too if you allowed her the opportunity. I wish I could rewind all of your clocks and give your parents the maturity and wisdom of an honest breakup all those years ago. Now you’re damaged, but it seems you also choose to be. My father was a serial cheater and the hurt I felt was outstanding, until I finally said “enough,” and let it go (that sentence took nearly two decades, btw). I came to realize my need to stay hurt was a trope that only continued to hurt me. I wish you clarity, and peace.