How can a couple have a tremendous amount of things in common for years, then one day he comes home and asks "What do we have in common?" ?

sage2021
And the only answer they both had was politics.
It was right around the time the transgender thing was on TV and social media and he started wanting to talk about that all the time. His girlfriend didn't and she couldn't figure out why he was so enamored with them when he was straight.
That's when they stopped having the same things in common and the little things he used to do and say to her also stopped along with the sweet terms of endearment he used to call her for years.
What could have happened that would change their entire relationship to the point of breaking up?
How can a couple have a tremendous amount of things in common for years, then one day he comes home and asks "What do we have in common?" ?
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