What does XSO stand for?

XSO stands for eX Significant Other

This definition appears very rarely

Other Resources: Acronym Finder has 2 verified definitions for XSO

Samples in periodicals archive:

Is it ever okay to snoop through your significant other's private papers, email, phone, journals etc.?

I keep having dreams about my ex-significant other (we have been broken up for six months). The dreams aren't about getting back with him; just about talking to him.

The Ex significant other joke thread. General NON-Automotive Conversation

(Ex) significant other is used in Emoticon. The word (x)SO is used in Emoticon meaning (Ex) significant other

Dear Miss Manners: My significant other told me she would like to continue the friendship but abandon the rest of the relationship. Although that took some getting...