"a boss has the right to fire anyone at any time"
In the US that's already the case and even the people who don't think that wives should be allowed to refuse sex from husbands seem to see nothing wrong with that. Well, except when someone is fired is for saying something factually correct but offensive.
In the US that's already the case
As OrphanWilde already pointed out, no, it's not. Even other than protected classes of people and protected reasons, trade union jobs and many public sector jobs are not employment at-will.
Speaking from personal experience, finding the right relationship can be HARD. I recently came across a rational take on finding relationship partners, much of which really resonated with my experiences:
http://waitbutwhy.com/2014/02/pick-life-partner.html
http://waitbutwhy.com/2014/02/pick-life-partner-part-2.html
(I'm still working my way through the Sequences, and lw has more than eight thousand articles with "relationship" in them. I'm not promising the linked articles include unique information)