Of course, he could
talk about his old losses when struggling with new ones. Say, when Sam dies, Jim might think back to the time he lost Gary. Or, if that's too badly in the middle of a crisis, perhaps our hero could again think of Gary, or of Edith Keeler, when wallowing in self-pity after "Requiem for Methuselah"?
It's probably mostly in his personality or upbringing that he doesn't discuss bygone things. In in-universe terms, that is.