Is it normal to cut off feelings for a stepdaughter

I'm 43, have a daghtr 19, 16 yr old stpsn, and a stpdghtr 13. 5 yrs ago, i fell in love with a great, succesful and lovng man. He had been raisng hz 2 kids, then 8 and 11, and was divrcd 8 yrs She ddnt want much to do with the kids til I shod up, then she wanted to becme involvd in their lives. She even tried to get my guy to come back to her "for the kids sake" whn she fnd out I was movng out here to be with him. grndama and neighbrs all kind of thght of the litle girl as tricky, manipltive She semed so sweet and I thght she would have a specl plce in my life, I felt i was the only 1 who belived in her.

now I cant stand the kid, she is horrble! I have been told that she has always been difficult. I worked so hard on her, but kept going back to her old ways. Her mom admited bad mouthng me to the kids, the boy and i have a very nice relatnshp, in fact he comes to me with any prblems, and i always supported his relnship with his mom, he knows how she is but loves her anyway, he knows his place is with his dad and I. The girl had appred to be doing beter about a year ago, (i was kinda proud, thght i hade made a difernce) it had been hard cuz she was stealng clothes and othr itms from my daughtr, lying about it, sneakng makeup g strings and pushup bras, and innaproprte clothng and i thought my postve renforcmnts on her good behavr had helpd. then we found out she was just playng us. havng sex, stealng, talkng crap about me, then she was on the phone when she was mad at me and said "can u beieve that bitch went through my stuff"? I would check her room then the next text said "sometims u just have to kill" after she had finaly earned a school trip and we thought she was ready for a puppy, she went back to ignoring me i didnt exist unles her dad were there, Over the years she would get mad and beg to go live with her mom, and tell her dad how great it was . he knew the mom was not the best parent but he let her for the sumr. it was just him his son and me. well it went on into the school year, and it has been so nice, no stress a happy peaceful home. so i guess the honeymoon between mom and daughter is over and she wants to come back well I dont want her back! my stepson came to me and doesnt want her to move back here, but I know she will i feel like my life and happiness are over. The kid came back to visit once and was so phoney it was disgusting! now i have been angry and depresed and look like a horible persn, the girl teling daddy how much she mises me ect... scuze me while i puke!! I have been tense and he senses it, he came by the house to get the birthday card for her that he bought, and told me he would see me later and to "quit b eing grumpy" I have been up since 3 am cuz now i am not slepng well becuz of this. Wht the heck can i do?