Iam so very sorry that you are in the midst of this terribly sad situation. I'll send hugs 'cause I am at a loss to provide comforting words...
Girlfriend, I think you have a good head on your shoulders and are looking at the situation from a humane and practical point of view. A sperm donor and a DAD are not necessarily one and the same. Ultimately, you must search your heart and decide what you must do and how you must handle the whole sad situation. Remember, there is always someone out there ready to jump on the band wagon and tell you how wrong you are ..so just brace yourself hold your head up high and know that your decisions were yours and yours alone to make and you made the very best decisions at the time and place you made them.
Again, I am so very sorry that you are facing this situation.... more hugs