Is it a red flag if he's friends with his ex?

My boyfriend is in touch with his ex who was the love of her life for 10 years, they were childhood friends as well.. He told her about me, she got upset with him and didn't talk.. He later talked to her and he told me that she sounded calm and was happy for him and me, even she's getting married and she blessed both of us for a happy life together.. My boyfriend said that she was a very significant part of his life for a decade so to have her best wishes as he begins his new chapter with me is very important for him.. I acted really cool and mature about it, but I got a little uncomfortable hearing it.. Should I be okay with this?

Is it a red flag if he's friends with his ex?
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