Is this worth talking to my fiance about?

My fiance has a 7 year old daughter and I have a 6 year old son. They get along pretty well for the most part and play together a lot. I've noticed lately that his daughter will take my sons toys that he brings over to share with her and not share them with my son. She won't give it back until she's done and has a huge issue with sharing her toys unless she gets bored with it. My son will get upset but will pretty much let her walk all over him because he likes her so much. This morning they were going to play a video game and when my son asked if he could go first for once she said if he did she wouldn't turn on the game (she knows how to turn it on and he doesn't). I was in the kitchen over hearing it all so I told her to let him go first just this once and she lied and said she needed to set something up and thats why she needed the controller lol. It's ridiculous but its constant and now my son is saying he doesn't like playing with her. He also told me today she told him she is allowed to say bad words and told him the bad words she is allowed to say. That bothered me. Do I talk to my fiance or is this all stupid and not worth talking to him about? Maybe I am just being over protective?