Sometimes I just leave people on read for a bit because I have more important things to be dealing with. This happens to me too sometimes with people leaving me on read,and I understand because there is almost always something more important than whatever someone is messaging about. If it were important, they would have told me explicitly or sent a meeting request.

I sincerely doubt everything you were asking this guy was very important, so perhaps you need to learn how to handle more of your own issues and ask more people for help other than that one guy. It is not that guy's job to do your job; it is your job to do your job.