Larissa's kind of like an anti-girl to Roger, which might actually be a good thing, since it means he'll treat her more like an actual human being than a challenge. A pretty high number of their interactions over the year have undoubtedly consisted of him trying to convince her to give Hamish a break on all the studying so they can do something Roger considers worth their while.
11-year-old Roger was THRILLED to find out that that one guy from the BBC was magical, too. Because he's him, though, instead of talking to Vicky about it like a normal person, he used it as an in to chat her up. He's not ashamed.
Seeing as he's not a big fan of detention or losing house point, Roger will attempt to censor himself around Leon.
Roger will be as polite as humanly possible to Anais, mostly because he's secretly paranoid that the Beauxbaton girls are reporting his every action to Fleur.
Other than Quidditch, there's not much Roger and Anzelm have in common, so I'd imagine they won't interact much. If ever they do, though, Roger will be nice.