As someone who has experienced depression for most of their life and has—for a time—thought that size fantasy might have been the cause or at least an exacerbating symptom of poor self-esteem, let me say this:
You are so much more than any fetish.
You may well find yourself obsessed with size fantasies to the exclusion of other interests and responsibilities. You might be devoting an unadvisedly large amount of time, energy, or money in pursuit of a fantasy that you can never fully realize. You may think that these desires will inevitably interfere with any real-life intimate relationship you might form with someone else.
I’m here to tell you that none of that is necessary. The human mind is immense place, and a million stories collide and combine there for our diversion and delectation. Some of it is bound to be gruesome. None of it defines you.