I forgot where I left my keys today. Almost as bad right?

Even though it would have been best for them to tell you, maybe it just didn't matter to them because they know that the real parents are who raise you, not who you are biologically from.

That sucks FYL! but as long as your "father" treated you with love and raised you as his own,then remember the good memories and know he loves you just as he would if you were his real son

I agree that forgetting they used a sperm donor 35 years ago would be upsetting, but if they loved you from the day you were born, you can forgive them, right OP?

I don't really see why this is a huge deal. It doesn't change who you are, fundamentally, to have different genetics than you previously thought. Your parents are your parents, no matter who contributed to your creation.

Well.. Maybe it isn't such a bad thing. You are their child whether it be biological or not

While that does suck not knowing for 35 years, that shouldnt change anything. They raised you and gave you love (i think) i dont see how this should change your view of them so dramatically

That kinda sucks. But if what they are telling you is true I'm sure they had good reason. On the flip side maybe your mom wasn't faithful? Either way, he raised you from a baby and so long as he did a good job I would consider him my father were I in your situation.

How do they forget something that huge? Amnesia? What is this? "All My Children?"

Speaking as someone who's the product of a sperm donor, it can be a very touchy subject for my father. Your parents probably just never mentioned it out of fear that it would effect how you felt about your father.