how do suppose Jake feels after he kisses Brett good night and she tells him she will not see him agian? Why do you think Hemingway abruptly ends the chapter with Jake going to bed alone?

I think that when it comes to Brett, Jake is devastated and relieved at the same time. Their relationship has been one of goodbyes. As for going to bed alone, it's almost symbolic of the lives each of these characters live..... each of them can be surrounded by people, and yet still be completely alone.