Jenn!!!!!! So I think that Ian would like James a lot and he’s probably known him for a long time, since he’s always been pretty close with the Connors and the Connors/Selznicks are neighbors/basically family and yeah James is a Selznick cousin ... anyway, when Ian used to date Natalie and has basically been in love with her his whole life, but they broke up and he still hasn’t quite moved on and when he finds out that she’s dating James, he’s gonna have a lot of mixed emotions, like equally jealous/really happy for them???? I think that Ian feels like he won’t ever be good enough for her, and he’s (accidentally) made her life a mess and that she deserves so much better, and that James looks like someone who actually does deserve her/will be able to give her her the life she wants.
Anyway, all that being said, I feel like he’s pretty good at hiding his jealousy, b/c his happiness for Nat honestly trumps that, but I can see where he might be a little quiet/short with James sometimes, but for the most part, I think he’d seem pretty chill about the whole thing