Kristina Talked Too Much!
I sympathize with Kristina's past, but it wasn't important that she crank open the lid of her sad history to Nick until she knew that he totally had genuine feelings for him.
Unfortunately, extremely troubled stories like that from women scare the living hell out of guys, and those stories sends them running to the hills. Nick was really uncomfortable with hearing about it.
Stop rattling the pots and pans, Ma! The boys are trying to sleep!