Long term chastity usually results in substantially increasing the sensitivity of a man’s penis. This is due to the physical and psychological effects of having his penis locked up.
Extended chastity trains trains the mind to associate erection with pain.
The result is the ability to ejaculate (due to the enhanced sensitivity, which often becomes something of a hair-trigger response) without attaining a full erection. It’s a rather pathetic sight, watching a small soft penis ejaculate and spurt cum, but it happens.
As his ability to reach full erection decreases, one of the other consequences is that he’ll start to prefer masturbation as a sexual release over sexual penetration. He will start to lose confidence in his ability to sexually satisfy a woman with his penis, and thus will eventually lose interest in it. He’s rather just masturbate.