I don't think I agree with this.

The "love is an action" idea comes from the fact that as a relationship goes through time, the intensity of feelings will fluctuate. In a marriage for example, there will be times where you feel as in love as you were during your honeymoon period. There may be times when depression, stress, fatigue or a host of other things can diminish the intensity to which you feel the emotion.

Does that mean you suddenly love this person less because you're not thinking of them every second thought, because you're not wildly fantasising about being with them every moment you're apart?

People who believe this tend to get divorced because they see a period of time when their feelings were less intense than before as a sign that they no longer feel love.

But people who have long successful marriages report one of the key factors as being realising that these emotions will wax and wane and wax again like the moon, and through all periods to remember the CHOICE to love this person through action. And the actions then can bring about the feeling.

For example a lot of female sexual desire is responsive, stoked by starting foreplay even if it's not caused by a wild desire to rip the pants off one's partner and fuck them. Instead, the actions of getting intimate, opening up emotionally, stimulating the body etc can wake the desire. (I'm not suggesting having sex when you don't want to but if you are intellectually interested or emotionally wanting to have sex but not yet physically aroused, a lot of women report starting foreplay as a means to get themselves physically aroused).

I think this is the same in regards to "love being an action". After all, the idea that feelings and actions are two separate things, is just a belief caused by dualism and not necessarily true. Feelings beget action. But action also begets and sustains feeling. You love your partners because of "who they are" but who they are is not a static thing. Being is a verb. To be alive is to always be in action.

The commitment to show your partner/s you care, that you want them, that you appreciate them, that is what helps keep the spark alive. And sure, you can be in a hospital bed for a month and the feelings remain. But do you think if you stopped doing any acts of love for your partners, that they would continue to love you the same regardless for how long it went on? After a while they would start to feel unappreciated and unloved, and start pulling away or feeling resentment.

There have been times in my relationship where emotion has been less intense, and times when it has been more intense than anything else in life. It seems to happen in cycles. But even during the times it feels less intense, I know that's not because I love my partner any less. It's not like he's stopped being my soulmate.

Likewise on his part sometimes he goes through depressive episodes where EVERYTHING feels more muted and dissociated. But he still knows he loves me, and that if we persist with the actions that help maintain and stoke love (as well as mental health treatment), he will get out the other side. Which he always does.

Also you can totally choose who you love (at least to the degree of being "in love"). I have had many opportunities to develop emotional affairs or even physical affairs with people I knew that if I opened up to in a certain way and started leaning on them more, or encouraged them a certain way, that I could end up falling for them and it would be hard to stop. And I stopped it before it went anywhere near that territory, or directed the affection into purely platonic territory.

TL:DR love is both a feeling and an action, and maintaining a strong love across time requires expressing that love via action. What those actions are will differ across time and circumstance.