But the assumption in that situation is that mc courted both but ultimately chose Bella. On that assumption that he also had feelings for Jill, that he was getting serious about her too, doesn't seem bad in itself.
Honestly, the mere fact that he courted them both had to be enough to get him into trouble (and Bella in this situation is at least as guilty as he is).
Now, from the point of view of the game, that choice will probably set up a future clash between the two friends, but it is a clash that should already have been there and has been postponed