这个不是固定用法吧,句意为：
After a few days with him,she could understand him no better than at first.
经过和他几天的相处,她发现她对他的了解并不比最初几天多多少.
she left her husband and his guest,for the most part,alone together,only to find that Jim hardly noticed her absence.
她在多数时间里都让她的丈夫和这位客人单独在一起,却发现Jim几乎没有意识到她的存在.
alone together 就是指她的丈夫和客人一起独处,不是固定用法