Nobody knows but me

I'm 20 and have been married 2yrs. I'm 7 months pregnant with my first child. My husband (34yo) is thrilled and so proud. What he doesn't know is that he is not the father: one of his best friends is. Neither the friend nor anybody else knows that my husband isn't the father. My greatest fear is that the baby -- which is a boy -- will eventually look like the baby daddy and people will start to notice. Other than that, I'm so happy to be carrying this man's child, although sometimes I admit I am really tempted to tell him it's his (I'm most tempted when he and I are together making love).