Was it Underhill all along?

Everything that happened - the womanising on behalf of Maurice and Jack. The humping scene in the woods by Diana and Maurice. The lesbian gettogether, the Grandfather dying and the alcoholism and general life of misery was it all enhanced by Underhill's evil curse.
And what happened at the end when Diana, Maurice and everyone were seperating. Was Diana pregant with Maurice's child and Jack end up cuckolded.
Was this at a time in the 1960s where they used the pill?