I'll go to an event and my ex will be there as well with some mutual friends.

She dumped me half year ago. We dated for almost 10 years. After the break up it was strict no contact except the day she send me happy birthday.

Should I ignore her? If I ignore her completely I may seem bitter. Maybe it's better talk to her as an acquaintance? What do you think?

She was my ultimate oneitis, I was totally crazy about her, even before we started dating. But now I can safely say that I don't want her anymore. I think is almost impossible for me to have a oneitis again, after having this one.

However it's kinda hard to stay indifferent towards a person which you shared most of your adult life. I don't want her back, neither I want to be her friend. Still she crosses my mind everyday. Any tip to maintain composure?