Well, huh, this is a hard question to answer without doing damage lol.

Here’s the most important bit: if you have to ask if something is an illusion, then it’s not an illusion for you. It just follows from the question. When something is seen as an illusion, it is no longer seen, it disappears. Let me give you an example: if someone doesn’t show up to a date and you’re angry because of that, as soon as you find out that they had a very serious car accident, your anger goes away, instantly. Was your anger an illusion? Well, no, it was real. But as soon as your other illusion (that this person is an inconsiderate schmuck) falls away, the anger dissipates instantly. There’s no more question of whether it is or it isn’t an illusion, it’s just no longer there.

So, ultimately compassion, or an emotional response to others’ suffering (maybe a better word would be empathy) is an illusion, yes, but this realization is one of the highest realizations, because it’s impossible to realize that until you’re completely alone. So only Buddhas don’t experience empathy. Empathy and compassion for others is basically the difference between a Buddha and a Boddhisatva. The last relationship is that of someone who can help other sentient beings realize their true nature, and it’s based on compassion. In complete aloneness, complete oneness there can be no compassion.

Just like all other illusions, it is real for as long as it’s there. It can take a very, very long time and a lots of tears to work through compassion, and there’s usually a layer of anger hiding behind it too. It is very emotionally hard to plunge into complete aloneness, which is why there are lots of Bodhisattvas and similarly self-realized people but very few enlightened people, i.e. Buddhas.

Compassion can also be said to be the stuff of the soul. As Osho said once, “the death of the ego is the birth of the soul”. It is. But ultimately, in enlightenment the soul needs to die also.

Now, all this talk applies to psychological relationships between people and the emotions they create. That’s what I mean by empathy/compassion. The physical acts of compassion (for example, holding someone in your arms, helping someone with advice, caring for a hurt fellow human, etc.) have nothing to do with it. One still does all these things, but with a calm and equanimous mind. It actually allows one to be much more effective.

So from the practical perspective, no, nothing in your emotional experience is an illusion. Nothing. What was an illusion and what wasn’t can only be seen in retrospect. All emotional experience must be lived through in its totality and not suppressed, and that includes compassion and empathy. This is actually the hardest part for most people, and it was for me.