What did he mean by the poem?

I'm pretty sure he meant that Javier was the son he never had.

The poem is basically exploring the love that Ramon had with Javier. Ramon loved Javier like a son. He was incapable of having children due to the fact that he is a quadriplegic. And therefore Javier was going to be the closest thing he'd ever have to a son.

The poem also explores that because he is in that condition that he is unable to do these things with him that a majority of fathers do with their children.

Just an interpretation.

Kaikki menee jonnekin ja menen kaikkialle

is it possible that his sister in love was the woman that he was in love with before the accident? and that she chose to marry his brother to stay close to him and javier could be his son?