Is shunning friends, turning a blind eye to them, and causing them distress, considered in any way part of Islam, doing so out of fear of falling into prohibitions more severe than adultery?

Avoiding the young man and lowering your gaze from him is the correct course of action in this situation, and it is not an forbidden abandonment; rather, it is an exceptional circumstance. Scholars have unanimously agreed on the impermissibility of looking at young men and boys with lust, to prevent temptation. Some of them explicitly stated the impermissibility of looking at beardless youths even without lust, as well as shaking hands with them or keeping their company. You should apologize to the young man without disclosing the true reason, and stay away from sources of temptation, occupy your time with what benefits you, remain steadfast in obedience to Allah, and persistently ask Him for well-being with sincere reliance and good expectation, and hasten to marry when the means are available.