I missed my girlfriend's abortion.
That's awful. Why did you missed your girlfriend's abortion?
I've been a retard and I was sleeping with the another person at the time.
If your girlfriend is having an abortion, you should be there to help her through this difficult time. Missing the abortion will cause you to have regrets in the future.
I know she's had an abortion and I don't care.
You should care because it was also your child and even if it wasn't about an abortion, a partner should be there for their partner. It is part of being in a relationship.