i have absolutely no experience in this area so im just giving a bystanders opinion (hope thats alright)

I always try to imagine how i would feel about something in order to determine the best course. We humans are all very curious about where we came from, thats generally the number one thing we begin to think about. So with that in mind you should expect that at some stage of your childs life, its going to want to know.

I would also take into consideration what it will be like to be a child at school with friends who are all talking about their fathers, being picked up from school by their fathers, doing things with their fathers etc, but not being able to explain about my own father because of not knowing who he is. I can imagine that I would feel pretty left out and maybe even a bit embarrased about it.

So If i was in your postion, i'd either try to find a close family member or friend who might be willing to act as a father 'figure' in the childs life so that they dont miss out on having that male influence in their life...perhaps an uncle, brother or a cousin.

The other alternative is to establish what sort of relationship your donor friend might 'want' to have in the childs life (if any) and see if you can come to an agreement about him having some involvement. I have no idea on how a donor man might think in terms of the child so perhaps its something to find out.