Am I being unfair in not seeing my dad?

Ok so this requires a bit of a story— when I was 10 my mum found my dad in their bed with his best friend (I’ll call him Jake). The story all came out in the end. My dad had been in a relationship with Jake for about 5 years before he even met my mother. He dated her, married her, etc all while with Jake. Needless to say my mum was devastated when she found out. She definitely tried really hard to keep a lot of this from my brothers and I, but we found out. My dad didn’t want any of this to get out and wanted to stay in the closet. My mum ended up agreeing to a divorce without telling anyone the real reason.

My older brother was really angry at my dad. He was 15 at the time and he refused to see my dad or even speak to him. My mum had to work more to support us because she didn’t want to have any help from my dad. So my brother took care of us a lot and he wasn’t very nice about our dad. He made it really difficult for our dad to be around any of us. I don’t really have a relationship with him and haven’t for years.

I’m getting married in December and my dad has reached out to me about wanting to attend. I haven’t seen him in 4 years. He’s still pretending to be straight and has had a few girlfriends over the years. I personally find that disgusting. I don’t care that he’s gay (yes he has admitted this before) it’s that he lies to women and especially to my mum whom he lied to for over 15 years with no intention of ever coming clean. He can’t love a woman the way someone deserves to be loved in a relationship. He’s just playing with their feelings. He broke my mum. She hasn’t been in a relationship since, she’s tried but she’s got a lot of distrust and things she’s still trying to work through. I hate what he did to her.

I’ve been in therapy since this whole thing began. My family has tried family therapy, but it really didn’t work at all. My therapist tells me not to feel pressured either way and to make the choice that will make me happy. I don’t have a relationship with my dad and I don’t really think I want one with that kind of man. But he’s my father and there’s a part of me that thinks I should have him there. My fiancé says it’s my decision and so does my mother (though I know she’d prefer it if he wasn’t there, but she’s a good mother and would support me either way).

I really just don’t know what to do. His dishonesty destroyed our family and we eventually picked up the pieces. I don’t want to have my family go through something like that again.

EDIT: my father has told me (in therapy) he is gay, not pansexual or bisexual so I am 100% certain of that. I also know that he still dates women while in a relationship with Jake. He has always been adamant that we never say a word about his sexuality and that is a major reason why we hardly see him- he’s afraid we’ll out him.

And while I do wish he’d come out, I will not have Jake at my wedding. There was a time when Jake was like my second father, but not anymore. There is a lot more too that side of the story. And it would seriously hurt my mum to have him at my wedding and I will not do that to her. So while I think it’s good option (thank you for the suggestion), it’s just not possible for me. I will consider talking to him about being honest though.