The sentence is very vague and unclear, even to a native English speaker. I think I understand what it is trying to say, though.
Lucile was saying: "other men live in things and events and emotions and the future. but he seems to know that living is something else...."
This sentence, though strangely worded, is trying to say that most men Lucile meets are thinking only about things, events, emotions, and the future. When we say we "live in" something, it often means that we are always thinking about that thing. For example, "living in the moment" is an idiom that means that you think about the present moment, and not the future. It seems to me that, to Lucile, thinking about things, events, emotions, and the future is a very common and possibly boring quality in other people. The fact that she can identify what they are thinking about probably means that most men are not new or interesting to her.
Meanwhile, the person she is referring to lives in something else, which means that they have more unique and interesting thoughts or mannerisms.
"Well, of course every one knows, really. But he lives it too."
I think that she's being intentionally mysterious here, which makes the sentence hard to interpret. But I think that the key point is that she doesn't say exactly what he "lives in". I think that this means that she can't quite understand where his mind is at, because he has a more unique way of looking at the world compared to the men she usually meets. Notice how the other men live in things, events, emotions, etc. Since Lucile doesn't describe Bellard in this way, he probably "lives in" (is always thinking about) something a bit more abstract and hard to put into words, which probably makes him attractive to her.
"l am not good enough for her," Bellard thought, and tried his best to prove that he was.
I don't know why this is said, but I think that this is a story where Bellard very deeply loves Lucile and she very deeply loves him, and the author wants to emphasize this many times throughout the story. I think this comment by Bellard is just another example of that, where he idealizes his wife and thinks that he is not good enough to have such an amazing woman like her.