This is true, talking things over makes me feel TONS better, but I have the hardest time getting him to talk. Mostly, an argument goes like this:
I voice my opinion
He gives me silence
I ask him what he thinks
He thinks about it for a long while
I get frustrated that he won't at least think aloud so we can have a real discussion
He apologizes
Wash, rinse, repeat.
Sometimes I truly believe that I know what he feels and thinks better than he does.
Like Beat (somehow) said, it´s a problem in S/N differences. I have the same situation happening with my best friend (yet another INFJ)
It could be that he does not feel comfortable about the way in which you voice your opinion. Are you straight and to the point, or you make a two-minutes speech? I prefer the first.
Also, try to mention something that is familiar to him while voicing your opinion. It will help a lot to get him respond faster, since familiarity -or lack thereof, is the first thing a Si dom will notice in a new situation or context. If it reminds him of something he already knows, or has experienced before; he will have it much easier to voice an opinion, out of similarity or out of contrast between what you said and his experience.
My friend, when we get to this part:
"I get frustrated that he won't at least think aloud so we can have a real discussion
He apologizes"
just says: "it is just like (something I, or we both did, a place I know, a situation I had been dealing with before)", allowing me to engage in a discussion faster. You can try this breaking point yourself.
And, the other way round, when he stays silent, I propose him to think about the situation in perspective, like "you see this happening now, how will this develop in the future (people´s reactions, changes in a situation)?", or "how does this (situation, event) fit into the present context?" to keep his interest in the discussion.