2 votes to go to the party. \:\)
Be brave and make sure OM sees you give W a big birthday hug and kiss too!

My suspicous side thinks that W expects you NOT to go, OM will be there, soon after that they will coincidentally start being seen together, the explanation will be that they 'clicked' at her birthday party and things just took off for them. How convenient!

Live your life while you are still living.
Riding the trail less traveled.