It seems to me the feeling or experience for which the term 'compersion' has been coined is real enough.
I just wish the word didn't come across as so utterly fake. I almost can't bring myself to utter it.
Why coin a new word, when existing words will do? There's the ancient Greek term, philia, which refers to a particular kind of love or affection or just plain old friendship. In particular, it's the desire for the happiness of another person, which works best when it's reciprocal. True friends rejoice in one another's happiness.
(In fact, I'd rather call my current way of thinking about relationships "polyphilia".)
If you don't like using actual words from dead languages, call it affection, compassion, grace, generosity, anything.
Just don't call it 'compersion'.
"Ignorance more frequently begets confidence than does knowledge" - Charles Darwin
"Mystical explanations are considered deep. The truth is that they are not even superficial." - Friedrich Nietzsche