Thing is that this isn't really an argunent about which point of view is right or wrong.

They are both right.

1. It is true that the child needs stability, consistency and doesn't need to be damaged by massive emotional upheaval.

2. It is also true that the mother has done somethng very cruel, selfish and irresponsible, the consequences of which have seriously affected the life of an innocent man.

Plus, as the child gets older, a bit wiser and a bit more observant, they will probably figure out that something is amiss, so the consequences may inevitably affect them too to some extent, though hopefully not during their formative years - especially not during puberty and such vulnerable emotional times.

The problem is that a decision must be made about what should or shouldn't be allowed to carry on, and though it must indeed be tough for the adoptive absent father (sigh) to come to terms with, he must accept that he is a fundamental foundation stone in the childs upbringing.

As has been said indirectly before, does he cease to love the child just because he discovers that the child wasn't created from his sperm?

Whatever the motivation, he made a promise to a child and that child relies on that promise being kept. If we were Lions, then maybe he could kill the child and eat it, favouring his own genetic issue, but he isn't and we aren't. We have consciously come out of the jungle. We are humans. We respect the rights and needs of children.