Yes, well those four elements are the brahmaviharas.
I've seen those described as being the right/appropriate/good attitudes for all social relationships.
So, it makes sense that they'd be identified as appropriate for a romantic relationship too, isn't that right?
As you said, his definition of upeksha seems non-standard.
But Dhammawiki's definition of them includes this:
TNH's definition ...
His suffering is your suffering and her happiness is your happiness.
... is at least compatible with the part of the standard definition which says that it is "not indifference".
I notice his answer doesn't mention self-view, identity-views, at all.
I think that the prescriptions from the suttas include non-craving, non-clinging ... non-hate, non-ignorance -- and non-self, "anatta", whatever that means.
Perhaps TNH touches on "non-self" in his definition of "upeksha" -- i.e. when he says that it's not about "my" happiness or "my" suffering.
It must be difficult -- and perhaps is part of a Buddha's genius -- to explain the Dhamma in a way that might be helpful to everyone, including people in a romantic relationship.
If his definition or doctrine doesn't seem to be exactly what you've seen taught to monastics, maybe 'cut him some slack'.
He doesn't define what "romantic love" is, and neither does the question -- whether it means "flirting", "dating", "marriage", "family", or etc.
He does say at the end,
The other person will no longer be the only object of your love because your love will continue to grow and embrace all of us. Happiness becomes limitless, and that is the love of the Buddha.
I think that's compatible with the suttas.
This other answer was careful to point out, "this is done without sharing your partner with others".
And the question said, "You don't want to share him/her".
But consider also this answer, which includes,
Look for someone who is compatible in four ways:
- Similar confidence in spiritual development
- Similar respect for self-discipline
- Similar respect for humanistic practices
- Similar level of wisdom
Perhaps you can see that a partnership or a family can do good together, help themselves and others too, be generous.
Buddhism loves everything without discrimination
I'm not sure where you get that doctrine. The suttas seem to be more about dispassion ... and discrimination!
So the idea of "loving a chair" seems a bit foreign, even antithetical?
I don't know much at all about Mahayana doctrine, though.
There's some privilege for "sentient beings", isn't there? I.e. you'd be more considerate of a "sentient being" than of a "chair" for example, wouldn't you?
I don't know, perhaps you're saying something about "Buddha nature being in everything", or something like that.
Another topic I want to mention is morality.
I think that morality is ideal (prescribed) and essential (in practice), and that morality exists for "householders" and "family members" as it does also for monastics, though the form of morality, the expectations or responsibilities, the definition of what's considered moral behaviour, differ.
But every person is or was a son or daughter, if you're not a monastic then you might be a spouse or parent too -- and morality is important in that situation -- and IMO the doctrine of the Brahmaviharas is part of the doctrine about morality, i.e. the proper attitudes in social relationships.
Which is a good doctrine, albeit a very general doctrine -- widely applicable because it isn't overly specific.