Father has a girlfriend. I don't know how to feel about it?

My parents have been divorced for five years. My mother has had a boyfriend for about four who I have grown to know and love as a father figure. My father has not dated until now. I found out yesterday. My dad who usually sees me at my moms house on Tuesday and wednesday from 5-whenever had been cutting his visits a little short to meet her. He says we come first but I feel betrayed and upset. My mom goes out with friends to a movie or to dinner not even once a week and my dad hasn't been staying with me while my mom is out till a litttle late like 10. I feel upset emotionally by tholis... Anya dvice as to how to cope!?! My dad is very understanding and great usually. Please help! What should I do?