I may be wrong but I think the fact that Chantelle is not a 'proper' celebrity still does bother Preston. I go back to the night when BB threw Chantelle the party in celebration of her new found celebrity status- Preston and Jodie had the most sour looks on their faces that night.
However, once Jodie was evicted Preston started to portray that there may be something more going on between he and Chantelle. He was getting way more touchy/feely with her in an attempt to get himself an interesting storyline. I think at that point he probably thought she had no chance of winning but he could use her to keep himself in the headlines/get himself in the highlights shows.
After watching his reactions last night I think we are seeing the return of the same Preston that we saw on the night of Chantelle's party. The same Preston who constantly grilled her with questions about her band in the first week.
Preston did say a few kind words to Chantelle last night but they were hardly convincing. What stuck in my mind was when Chantelle said she couldn't believe she had survived eviction against George and Dennis, and Preston replied: "Yeah, and you're not even a celebrity". The look of resentment on his face as he said it said it all really. As a huge Big Brother fan, Preston knows exactly what's going on and probably realised after last night that the only winner will be Chantelle.