I'm addicted to something an it might damage my relationship what do I do?

Go to rehab?

Depends on what the addiction is. Eating too much chocolate?

How is it affecting the relationship?

Some addictions will kill you. That's worse than affecting a relationship. Regardless, you need to go to an appropriate rehab to break the cycle of addiction.

You need to get the proper help, so where are you in the world, and what are you addicted to?