What is the ruling on an unmarried young man wearing a men's "string" (thong) for the purpose of comfort in the sensitive area, and does this constitute imitation of women?

It is not forbidden for you to wear the mentioned underwear if it is specific to men, and there is no difference in this between an unmarried and a married person. What is forbidden for a man is to wear what is specific to women, just as it is forbidden for women to imitate men in what is specific to them in its type, form, or what is predominant in their attire.