No, he isn't a transvestite, either.
A few details before I get to the meat of it (and this will be long):
My mother is in her mid 50s, and the man I call "father" is her third husband, he's in his mid 40s - they've been together for about seventeen years. I am the eldest child, hovering at around 30 (product of the first marriage). My siblings are all around twenty, and are products of the second marriage.
My mother has always been incredible, and did a great job raising us. Not overbearing, not too lenient, always able to provide for our needs, etcetera. I really cannot find fault with this woman.
Her first husband cheated on her before I was two years old, and after they divorced he married the woman he had the affair with. Her second husband cheated on her (with my cousin, who was 19 at the time) after my youngest sibling was born. They divorced shortly after, and he hasn't been seen since. (Thankfully my cousin "grew up", and her relationship with my mother is good now.)
When my mother got married for the third time, I proudly told my friends that despite the fact that he had not contributed to my DNA, this man was my "real" father. Their relationship was great. He was a "dad" to us kids. He was good and smart and wise and strong. If they argued, they were always able to work things out.
Turns out, as of a few months ago, he's cheated on my mother too. I only recently found out. My mother is a wreck. This really did hit her out of the blue. She wants to get professional help, to learn if it is possible to rebuild their marriage. My "father" is waffling between being utterly manipulated by his mistress and wanting to work things out.
So, my view of my "father" is shattered. No longer wise and strong, he is suddenly weak and stupid in my eyes. I am aching with grief for my mother. She has requested that I not tell my dad that I know (for now, in case they can work things out). I only see them a few times per month, and I am having difficulties not being all strange towards him (in person and on the phone). I find that I cannot forgive, as my mother seems to have. I am not a violent person, however since learning this I constantly have the overwhelming urge to punch my "dad" and his mistress repeatedly. (I am not in danger of doing so, I know that it won't "fix" anything. That is just my emotional state.)
I need help. How can I deal with this, or get over it? Anyone who has been in a remotely similar situation, how can I offer support? One of my siblings knows, she's torn apart, and I don't know what the hell to say to her. I'm supposed to be the smart older sibling, and I feel like I'm 11 again.
I'm too old for this shit. So is my mother.