Isn't Istikhara a means of bringing psychological comfort? And if there is no good in associating with this young man, then why has attachment to him increased with his increasing turning away? Is this a punishment or a trial?

Istikhara is a request for what is good in permissible matters. It is a submission to Allah's command and seeking refuge in Him, the Exalted. It only brings comfort to those who are content with what Allah has chosen for them. Attachment to something that was abandoned is not a result of istikhara but rather of a lack of contentment. Any affliction that befalls a servant may be a trial or a punishment. One must be patient, content, and submit to what Allah has decreed and predestined. "And perhaps you dislike a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah knows while you know not." Furthermore, despairing of something helps one forget it and brings peace of mind from it.