I'll back up a Fi-dom also. He sounds like an ISFP guy I used to know - moody, spontaneous, very loyal. Whenever one of his friends would fall into some trouble he went out of his way to try and help him or at least offer his services in doing so. That arguing about opinions - P-types tend to hold stronger opinions than J-types I find - but it is perhaps because you're a Ti-dom and he is a Fi-dom that you don't have an opinion concerning some things that interest him because they haven't caught your interest. And yes, SPs are notorious for not being interested in personality profiling - I think the ISFP section of this forum is the most depopulated one 

I find that people openly expressing their feelings to others, projecting that image of being moody, tend to be dominant in Fi.
infjs can be moody but people around us would never know
I find that people openly expressing their feelings to others, projecting that image of being moody, tend to be dominant in Fi.