Tink is right; if you have a chemical imbalance, anti-depressants should balance it out. Estrogen can, in fact, exacerbate depression; on the other hand, if your depression is precipated only by gender dysphoria, I suppose HRT could be of some assistance. However, to clear up misconceptions: SSRIs (selective serotonin reuptake inhibitors), the main medications used to treat major depressive disorder as well as myriad other psychological maladies, are non-addictive. They have no known long-term ill effects, and do not lose their effectiveness over time. They simply block the reuptake of serotonin, a neurotransmitter that aids in the regulation of mood, into the synapses. This allows the serotonin to remain in the receptors longer, naturally elevating mood. There is no dependance to be gained.
Also, there is no substitute for good, old fashioned psychotherapy. Working through your problems is always the best solution; it's just nowhere near the easiest. Good luck, Alice.
Dino