My Husband and My Stepdaughter Relationship Grosses me out

I am a Mother of four, Two Daughters , One Son and one Stepdaughter. My Step Daughter comes over most week-ends and most of the summer break. My Husband and her cuddles on the couch all day long, she even puts her legs between his. They are always cuddled  up so much that if someone walked in and saw it I would be embarrased. She looks like the wife  with the husband and I am just a friend sitting way at the other end of the couch. There display of affection grosses me out. Now he has two daughters by me and he is not as nearly as affectionate with them as he is with the 13 year old sexually active step daughter. I dont think incest is going on but I am not sure either. I told him the behavior is inappropriate and I will not stick around to see another second of it. If it makes me uncomfortable it has to be wrong. I even asked others and they have stated that its inappropriate. He thinks Im jealous but that is just not true. I have been her step mom since she was three and this was not a problem when she was younger. Now that shes older and sexually active its gross and inappropriate and there actions have moved up some levels since she was a little girl. My mother notices it as well and I have never expressed it to her. I have anxiety and hoping this is not one of the mood swings or paranorah brought on from anxiety. But I am about to divorce this man for this reason. Has anyone else ever had this situation. Please comments and opions are needed.  HELP ME.

[plomeli]

Wow I think you should trust your insticts, they are usually right. Can you talk to her also and tell her,  I know you love your dad and your dad loves you but somethings are inappropriate??? Tell your husband that you are his wife and that he has been with you for a long time and because of that he should trust what you are telling him. Well hope this helps. Good luck.