Is the feeling of envy towards the difficult lives of others, and wishing that they be afflicted with a tribulation to alleviate the feeling of loneliness in suffering, considered envy for which one is held accountable?

The envy you feel is not commendable. While it may not be a sin in itself unless accompanied by forbidden malice (hasad), it is a strong gateway for such malice to enter the heart. Your joy at the misfortunes that befall those who are blessed is blameworthy. To rid yourself of this, act upon the Prophet's advice to look at those who are beneath you in worldly matters, and frequently ponder over Allah's blessings upon you, striving to be grateful for them. Increase your supplications, asking Allah to help you be grateful for His blessings. And know that any affliction that befalls you is due to your sins, so increase your seeking of forgiveness and repent to Allah.