I support the use of finasteride for guys with elevated DHT, which happens frequently while on TRT. You are not on TRT (right?), so i question your use of finasteride. Yes, it will help to save your hair from falling out, but you need to balance the risks with the benefits. The benefits are clear, you keep your hair (or at least slow down losing it), and you are seeing the risks with sexual side-effect and other low T symptoms.
Finasteride is a powerful drug for blocking conversion to DHT, so if you are going to use it, you need to titrate the dose so that your DHT levels are within the normal range. In your case, that would probably mean no finasteride unless you were somehow high in DHT prior to it’s use. In that case, the required dose would be much lower than 1mg/day.
Regarding the interaction of finasteride/DHT/E2, it’s difficult to say. The steroid hormone cascade is much more complicated than the simplistic charts make it out to be. Disrupting one hormone in the cascade of hormones can have unpredictable effects on the delicate neuroendocrine balance within the brain/pituitary/testicles (as well as adrenals and other glands).
Oh, your SHBG is within range. I’d kill for SHBG levels that low. It’s not the root of your problems. I’d focus on the low DHT.