I'm not so sure. He's actually still a virgin as of day 7 (this is revealed on Gil day 7 if you don't sit with him on the bus iirc). Would he really lose his virginity to Talbot of all people, who he seems to have no romantic/sexual interest in whatsoever in the other routes? Maybe since Lars is his ex he's extra jealous of him and Walter, but idk. It's possible they were kissing or something, but I very highly doubt it was sex. Or it could even be a red herring and Walter misinterpreted things and it was just an argument.
