I really don't see a scene where it's implied that Picard slept with Kamala other than her telling him that she has permanently bonded to him, and maybe the closing scene where the ambassador says 'how did you resist?' and Picard says nothing. That could either mean "I didn't (resist)" or it could mean "I barely was able to resist. I'm miserable about this and don't want to talk about it," which is how I've always interpreted the scene before.
The look of shame on Picard's face as Kamala was getting married and Picard's non-answer to the Ambassador were all I needed to see. Throw in Picard's awkward discussion with Beverly the following morning after the cut-away from Picard and Kamala. The writing, directing, and editing were all done with surgical precision. And Patrick Stewart's acting afterwards are what sends the subtle, unspoken signals afterwards. It's all the the facial expressions, line-delivery, and -- like I said -- the non-answers.