Can someone please explain to me ( in simple terms ) what it means if someone calls you their " fickle muse " and I don't want a Google answer ... I want to know of it's an insult or no?

Insult be damned. A muse inspires but a fickle muse inspires like a zephyr.

And I chose thst word because while a force 10 gale is a "strong wind" a zephyr is a fickle wind. It's kind of playful and nice.

Your friend has intelligence and imagination. Accept the compliment with a smile.