Expression: "With what relation?"

[Tom]

Hi

Do you find the red sentence correct and natural? What are the other options?

A husband and wife get divorced. A few months later the woman's younger brother gets married. She sends the invitation card to her ex-husband and waits for him anxiously. He does not turn up. She makes a phone call to him after the marriage ceremony and says:

[Yankee]

Hi Tom

That sounds odd to me. How about this:

I didn't think it was appropriate for me to come (since I'm not his brother-in-law anymore).

To me, however, it would have been most appropriate to tell his ex-wife in advance that he would not be coming. Explaining why he didn't attend the wedding after the wedding is over suggests a different sort of conversation to me.
.