To be a writer, it's not enough to just love writing. You have to have a constant love affair with it. To want to sneak in writing whenever you can. Even if only for a moment to take a few notes.
As your writing matures, and becomes a steady part of your life, your urge to write matures with it. Like in a long relationship, the love affair takes another form and gains bigger depth, but it doesn't stop. It's always there as a constant flow of inspiration and passion, and writing is the same. You must grow with writing like you grow with love.
I sometimes hear from younger writers that they find writing addictive. I suppose it has some truth to it, but I never felt like that myself. Maybe because writing has always been a natural part of me, and how can you be addicted to yourself? If so, it's probably not that healthy.
I will say, though, that during the periods of my life where I have not focused on writing, I have had the feeling that something fundamental was missing. It wasn't something I couldn't live without, because I could, I just didn't function very well.
That's more like a love affair with someone you want to spend the rest of your life with. Someone you want to grow old with and share every little part of yourself with.
It's true love based on the passion coming from taking the long way home. A surrender to something bigger than you that carries you through life, and allows you to carry it.
To put it simple: It's writing.