Does lending money to a friend for the purpose of working in a commercial insurance company constitute an ongoing sin as long as the friend continues in this work, and what should the lender do to atone for this sin?

What the questioner did by seeking forgiveness and feeling remorse is sufficient for him, especially since he has forgotten the type of forbidden work. The ongoing sin does not apply to his case, because whoever repents from a sin after having committed its cause has done what was incumbent upon him, even if its effect remains. This is in accordance with the saying of the author of Marāqī al-Suʿūd: "Whoever repents after having committed the cause, has indeed done what was incumbent upon him Even if its corruption remains, like one who retracts from spreading an innovation that is followed." He should now advise his colleague to look for another job and to leave working in this forbidden field.