Looking at the early events of the evening from a human perspective, I think it’s in keeping with his character that he would have found himself conflicted when coming across LS.
He isn’t some loner who hasn’t been able to form relationships or any sort of normal life. He had a stable job, a family and a home. He had friends, did normal social activities day to day etc. He did have another side to his personality, as we know - but I think (I may be wrong, of course) that was a complete surprise to those who knew him. He was letting this ‘secret’ side of himself grow in confidence, that’s for sure.
He hadn’t (as far as we know) involved any direct contact in his previous perversions. This was something new. I think by offering to help her, he was taking time to assess whether or not this ‘new’ step in his perversions would work. Hence why it wasn’t an immediate thing in the Endsleigh Centre. It wasn’t a plan as such that he was aware he was making, but a development of confidence in the emerging chain of events.