Let me quote from Tim Keller’s book Counterfeit Gods

We think that idols are bad things, but that is almost never the case. The greater the good, the more likely we are to expect that it can satisfy our deepest needs and hopes. Anything can serve as a counterfeit god, especially the very best things in life.

What is an idol? It is anything more important than you and God, anything that absorbs your heart and imagination more than God, anything you seek to give you what only God can give.

A counterfeit god is anything so central and essential to your life that, should you lose it, your life would feel hardly worth living. An idol has such a controlling position in your heart that you can spend the most of your passion and energy, your emotional and financial resources, on it without a second thought…….

If anything becomes more fundamental than God to your happiness, meaning in life, and identity, then it is an idol.