I generally don't like watching love interests fucking (sucking, jerking etc) other dudes, unless you can completely avoid them after that, but Zoey was my favourite too, so that made it worse. As I see it she's the only one the MC had an "interaction" with so far, she's flirting with him, but in this scene she's a slut jumping on a cock, just because someone else told her to do it and then she basically said that she had fun and wants to do it again... It doesn't matter that there wasn't any penetration, she enjoyed making another guy cum. It's not that much different.