Would you be upset if one of your parents’ was spending a lot of time with your ex partner?

After my brother and his wife got divorced , cuz she decided she no longer wanted to be married and broke my brothers’ heart , My Dad has been spending a lot of time with her and acting like it’s no big deal. I was upset that my father was doing that to my brother and told my father that he is a selfish piece of shit to be doing that to your son. Am I wrong?
Would you be upset if one of your parents’ was spending a lot of time with your ex partner?
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