Most US employers absolutely can legally fire an employee because of who they fall in love with, as long as the action isn't based on a policy which disproportionately impacts a protected class.
It's in court right now.
And it always will be.
https://www.employmentattorneyla.com/blog/2017/06/what-are-c...
No way. Two people falling in love is not in the same category as someone saying public things.