When their son?s death triggers his wife?s mental disorder, a man soon discovers his mistress will do anything to get the grieving mother out of the way, and he must choose: his wife or her alter.

'It was all in his or her head' like stories have been done to death (pardon the pun...), be very careful when pitching this. The whole, the wife is the mistress, last-minute twist will have very little impact now day and age.

Stories are about action not choice making, what happens after he chooses? What does he do? What does the wife/mistress do?

What kind of man is he? You need a better description than that for your main character in a logline.

The story is the choice.

A man wants to help his grieving mentally ill wife but is undermined and pressured to leave by mistress.