Should I go to my “ex’s” birthday party?

We never actually officially dated and he officially rejected me a week ago. We’ve been friends for a long time up until the last year where we were basically in a relationship in every way but name. He told me that he valued my friendship and wanted to stay good friends. I immediately took space from him. I planned on keeping it going until end of June/beginning of July tbh so that I can focus on myself since I was more invested in him than he was me and get over any lingering attachments. He asked me today if I would go to his birthday party (it hasn’t even been a full week) next month and I’m not sure if I should or not
Should I go to my “ex’s” birthday party?
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