Is it bad to think sexually about your stepdaughter? I mean, she is not bloodrelated right. She just asked me to tell her which bikini I liked best

Is it bad to think sexually about your stepdaughter? I mean, she is not related right. She just asked me to tell her which bikini I liked best. A guys opinion is what she needs, she said. But fuck me, then she stripped down and next thing I know I am staring at her cooch.