I think you should attend your daughter's birthday feast. It's her special day and whatever is going on with your wife should be set aside just a wee bit. You don't have to stay a long time, but it would mean a lot to your daughter if you attended, i.e., long enough for her to see her cake and open her gifts.

Just my two cents.

Sit quietly, the answers will reveal themselves when you least expect them to.
The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.