in act 2 why do gerald and sheila act "bitterly" to each other ?

It is in Act 2 that Gerald's relationship with the girl who called herself Daisy Renton. He was intially acting with honour as she was starving and homeless, and being lewdly pursued by Alderman Meggarty, formerly considered a pillar of the community. However Gerald confesses that he and Daisy had a sexual relationship. Sheila as his fiancee is shocked by this revelation, as are the other family members.

Consider the effect of their reltionship in terms of their being constructs; Sheila, the impressionable young, converted to socialsim, Gerlad, the son of a lord and lady, firm set in his interests of capitol. Their bitterness towards each other may represent the contrast between these two radically different polical ideologies.