I don't think you are "merely" jealous. I think it is inappropriate and almost abusive to the child, who has no choice and is being "taught" that sleeping with grown men is okay; not all grown men she encounters will be like her father but she is being "taught" they are! She can get very hurt when she becomes a teen and now, when/if the father starts to sleep elsewhere she will have a bad time because she's accustomed to him sleeping with her.

I have a good friend and her twin brother married and had a child and the child slept with the parents and they couldn't get that solved and she got older, etc. and it became such a mess they separated/divorced.