WVU, if people listed to half the crap in this forum nobody would be married and everyone would win 85% of their bets.
I married my second wife in 1998 and she had a 4 year old boy. We quickly had three kids of our own and everything is great. Have there ever been issues between myself and her son? Sure there has, but it has never been anything major. Her son will turn 15 this year and has always been a good kid. His father wants him to go and live with him but he refuses to do so, saying he is happy living with us.
I'm pretty sure there are plenty of examples of when the kid says you're not my father but that's not always the case. Every child is different. I will say that the hardest part is that I feel a little different towards my own kids and him. I try and keep in mind though that it's not his fault his parents divorced and treat him equally.
Make up your own mind and do whats best for you. Good Luck in whatever decision you make.