My wife and him are like water and oil

My daughter of 7 years old calls my friend daddy and refers to me as uncle. This my friend has been a part of our family long before our daughter was born, in fact he's practically like family, he comes to our house almost all the time and my daughter likes him a lot. He isn't married yet and he's 42 years old, he's comfortable enough so money isn't his problem, he claims he hasn't seen the woman of his dreams. My wife and him are life water and oil, they don't meet so I can't think of my wife doing anything with him and I also can't say 7 years is too young for a girl to know who are real dad is. Although, i work offshore so i'm hardly around but I don't think my wife would cheat on me. Please this matter is serious and it's gotten me confused. I don't want to accuse my loving wife of infidelity because I have never caught her in the act  but how do I explain this mess. Please Mamalettes, help me.