Stacey,
We must never judge people from their past. For one, we are not in their shoes, so who is to say that you would not done the same,in an identical situation. Two, Salvation and repentence would have been nul and void if The Lord kept judging us from our past.
I understand that your feelings may have been hurt from knowledge of the past. However, it did not happen so don't let it get you angry or hurt. Your are here, so enjoy life to the fullest now. I have also used the past to justify negative actions, then i usually find it foolish to do that, it really makes no sense to lose joy over nothing. Why should I err or sin because of someone else's short comings?
Regardless of what or whom your parents were, the bottom line is they are still your parents. It is better to reason with them as to understand the situation at that point in time. Empathy is LOVE, and Love is the greatest commandment. Try to put yourself in that situation and see what you come up with.
Though it may be hard to connect with them because of previous circumstances, you owe it to yourself and your future children to at least have a relationship with them. Don't deprive or rob yourself of this opportunity. There are many people in the world who wish they could have known both their parents.
So put away anger and don't be bitter toward them. Instead forgive them for your own sake, for your own wellness wholeness and happiness. Whether they are together or not, love them both the same. It is not easy living in this cruel world, don't add additional stress and inflict negativity to your own life.
Indifference is a an emotion of unresolved matters. You may feel it is not affecting you, but deep down it does and in ways you don't realise. Trust me i know, I am champion indifferent. Holding hurt and pains inside will destroy you, and especially when it is against your parents. Because, not honoring them and being rebellious in any way leads to your destruction and death.(that's bible)
Within your words there is hurt, disappointment and pain. Don't hold it in. Talk to them with all honesty and explain how you really really feel. Be respectful and they will have to listen.