She has two responses depending on whether you were serious about dating her.
If you were not on her route she's upset but largely forgives both of you but still hurt at the lying. She calls Bella out for being so judgmental during their friendship despite doing something largely immoral. MC has a brief scene where he apologises to Jill but she's understanding, the talk about not being right for each other and Jill's somewhat friendly admitting she had doubts about MC.
If you were on her route she's fairly heart broken, calls Bella out like above but asks that Bella not talk to her for a while, she isn't half as forgiving and whether they're friends in the future is up in the air. Jill also has a scene where MC apologises. You can kiss her in this scene and make it clear you were into them both but chose Bella. MC cries in this scene over hurting Jill. In this route she frequently mentions falling for the MC.
In both "routes" Bella indicates she'd break up with the MC if Jill asked.