In today's society , the idea of the 'nuclear family' - mum , dad and 2.4 children - is rather outdated. Whilst the majority of children still tend to be born to a heterosexual couple who usually register the birth together - whether married or not - the family unit in today's society is made up of step parents (with divorce rates on the increase) , grandparents , homosexual/lesbian couples etc as well as the so called 'norm'. What difference does it make if the child or children do not live with both biological parents ? As long as they are well loved , secure and nurtured then surely that is what is important , not who is the biological father ? Your friend obviously knows what he is letting himself in for and I am sure he realises what his responsibilities will be. If he can accept this , then you should be happy for him. Being able to concieve a child biologically does not make you a father/mother. Pacing the floor in the middle of the night with a sick child in your arms , comforting them when they are distressed , mopping up their tears and providing a safe , loving home is what makes a father/mother. It doesn't matter who 'planted the seed' so to speak. I have friends who are step parents and do not see at as an issue of who got in there first. It clearly wouldn't work for you by the sounds of things but who's to say if you met the right person , fell in love and they happened to have children that your feelings might change. Do you accept that a partner you may have , may have had other sexual partners before you ? Or do you find it hard to get your head around the fact that she may have been with other men ? Your friend obviously acknowledges that this woman has a past and is comfortable with it , so be a good friend and support him.