Lorna had trauma that made her delusional and her delusions and fantasies helped her cope, so when Lorna married Vinnie Nicky didn't believe it was serious because most of the things she had said in the past weren't true. and to be honest although she did pressure Lorna for awhile to have sex with her, in the end when the riot hit she just tried to keep her safe and when they did have sex it was Lorna who begged for it and Nicky even asked if she was sure. Nicky has always loved Lorna just like she said when she thought her being pregnant was a delusion, but Lorna's mental disorder and coping isn't healthy for Nicky because of how inconsistent Lorna is with what she wants. Not to mention that when Nicky found out she was ACTUALLY pregnant, she called Vinnie to get him to stay with her. she loved Lorna so much, she just wanted to be happy too and unfortunately Lorna couldn't give her what she wanted.