There is a line between an amateur and a pro, and it isn’t making money, it’s realizing that one’s product is distinct from one’s person.
If a writer asks for your opinion, give it to him honestly. You do both your judgement and his work a disservice by pandering to the conceit of his “feelings.”
And beyond pointing out the wrongs and weaknesses, one might try to find what the other is attempting to do, and urge him to do it better; perhaps telling him to avoid X, Y and Z until he’s got A, B and C down.
But it is important, if one’s criticism is to be useful, to tailor it to the parameters of the work in question, and avoid the cliche’s of critique (i.e. “show not tell”) which, in a subtle way, exert a homogenizing influence on the creative process. Each work of art really only works well when it is in tune with itself. This is what makes writing so damn hard, and why critiques often miss the mark.
In the end, if his desire to be a good writer is stronger than his desire to be liked, he will buckle down and put in the time and effort required. And, should you strive to make your critique a work of art, then the art of writing itself will be enriched by your contribution.