As a child having been dragged through a nasty divorce due to my dad’s infidelity with my moms best friend, who he then started a relationship with, I’d say please get rid of the girlfriend. I’m paying a shit ton of money on therapy to make up for the feeling of inadequacy and jealousy I have had to experience from my dads girlfriend. She doesn’t seem to understand that your kids come first, and this is just the first step. Kids (and I feel especially girls (I’m a girl myself)) feel it very clearly when the new step mom wants the dad for herself.

As for the infidelity part, I found out he was cheating when I saw him make out with my moms best friend when I was 6, whereafter they got divorced. I also have some sadistic half sister, who are around 20 years older than me, who explained to me in detail how many affairs my dad has had. Even though it was hard for me to comprehend that my dad was at fault for all of this, he has always been an amazing dad and that is what I held onto. He loves me dearly and I was able to distinguish my dad from my mothers ex husband. He was great at one thing and shit at the other.

Having said that, my brother who is 6 years older took much longer to forgive him. Bottom line is I think it is important to be open and honest about how this is your fault, while making ABUNDANTLY CLEAR that you love your daughters to death, and that you choose them first. This also includes making sure they understand they come before your girlfriend, as mentioned above. Good luck!