12 years is not a small relationship. Your mind and heart were attached to this person for a very long time, so what you are feeling right now does not mean something is wrong with you.
Honestly, after such a deep breakup, many people feel exactly like this — thoughts looping in the mind, no interest in work, inability to focus, suddenly feeling low, listening to sad songs, feeling okay one day and completely heavy the next day.
Right now your system is still emotionally attached and trying to adjust to a huge loss. That process can take time.
But since it is affecting your daily life and inner peace so much, I would suggest you do talk to a mental health professional instead of handling it all alone. A trauma informed psychologist would be the right person to start with.
I generally tell my clients who go through breakup and are grieving that healing usually does not happen by forcing yourself to forget someone. It happens slowly — by talking, processing emotions, rebuilding routine, and reconnecting with yourself little by little.
Next Steps
For now, try not to stay alone with your thoughts all the time. Keep some structure in your day even if motivation is low. Meet people you trust. Eat and sleep properly. And when the sadness comes, don’t fight it too much or judge yourself for still missing her.
You are grieving a big emotional chapter of your life. Be patient with yourself. This phase can improve, especially with support.
Health Tips
Feel free to reach out to me whenever you feel comfortable, if you would like to discuss this further or need support in understanding what you are going through.