Men who have discovered a child you raised isn't biologically yours, how did you find out and what did you do about it?

My partner and I had a huge falling out early at the end of our first year together and we split up for a few weeks (mutual) to let things calm down get our heads sorted and we'd see where things went from there.
Well she got drunk and went back to her ex (here by know as dick) and one thing lead to another and she slept with him. Well guess what happened.
She called me the next day and told me what happen and I have to say I was angry but more disappointed in her. fast forward a month and shes late, she panics, she gets a test and yep positive. She let us both know.
She decided it was best to get back with her ex for the sake of the baby (was his but the timing meant it could have been ether of us)
Fast forward 8 more months and she gives birth to a beautiful baby girl. I was happy for them but she confided in me that things hadn't been working out between them but was only holding on for her daughter sake. Few months down the line she finally has enough and breaks it off with him and we start talking again, we spend some time together and I meet the girl who will become my daughter.
Over that all took place over about 8 months before we decided to get back together to add some stability to her daughters life (as they were spending a week each with her at the time then swapping) and since then dick has been a constant hassle in our lives we've tried to keep him involved in her life but he doesn't seem to want second best its everything or nothing and my partner decided nothing until he got his life sorted and he agreed.
Its now almost a year later, we're getting married (when we can get the money together) and her daughter now calls me daddy. We'll always be honest with her that I'm not her biological dad and its up to her whether to call me dad or not when she's old enough to understand. We'll never stop her from getting in contact with dick if she wants too.
But when she called me daddy for the first time it made me feel so happy that I almost broke down.
We're never wanted to cut dick out of her life and if he feels that he wants to be a part of it again and my partner thinks he's stable enough to handle it we'll take her to meet her dad again.

/r/AskReddit Thread