I'm so sorry that neither one of your parents was decent and loving. It sounds like your father (or “sperm donor” as many fatherless daughters dub such men) had no desire to be a dad. He was happy to accept an easy out from your mom. Sadly, he probably saw red flags that she would be an unfit parent but selfishly bailed on you anyway. Unless he's changed dramatically since that time, it's safe to say that he's a person of extremely low character.
If choosing to continue a relationship with him, you should have some blunt conversations about his behavior. At the very least, he should provide you with an explanation of why he left and offer a sincere apology. If this doesn't happen, I see no reason why you'd want to keep him in your life. It would be much wiser and much healthier to put your time and energy into cultivating other relationships--ones that are based on mutual trust, kindness, and respect.
Some fatherless daughters use the term “sperm donor” for their biological dads to jar them into reality. It helps them see that this man holds no lofty position in their lives just because they have DNA in common. Instead, he's merely someone who had sex with their moms. He never took on the role of daddy, which requires enormous amounts of time, commitment, and sacrifice.
While it would be incredibly painful at first, accepting the fact that you had neither a loving mommy nor daddy would bring peace over time. Acceptance eliminates the stress we create for ourselves when we wish things were different than they are. The spiritual writer, Bryon Katie, says it perfectly: “if you argue against reality, you will suffer.”
You have experienced a lot of heartache in your life and abuse that no child should suffer. I hope that you've sought the help of a therapist. If not, please do so. This is too much for someone to handle on their own. A professional can give you much-needed guidance and support.