It's tough, living with the feelings of your own needs being inherently wrong - Fugo knows that it's not the way to do so, either. But even if he recognises those feelings as completely irrational, he can't stop himself from freezing up whenever he notices his own arousal, and neither can he stop his breath from speeding up, nor the dire need to somehow rid himself of it altogether.
Even as he tries to normalise it to himself in any means he can think of, time and time again, his emotions become too overwhelming far too easily.
To him, Bucciarati is the only person he can trust. It's both reassuring and scary, thinking about how the only person he can trust also has such urges. Such urges as the person who ruined his life, and, sometimes - unfortunately - such urges as his own; so, confronting him about the ryhthic sounds he hears sometimes in the evenings becomes inevitable.
As such, over several evenings, Bruno helps Fugo to slowly ease into his own sexuality and make peace with his feelings, staying patient - no matter how many times it causes him to be mere moments away from the release that keeps building up, forcing himself to ignore it and comfort Fugo to the best of his ability.