英文問題Because once John committed himself to putting his life back together?

語言裡面,很多意思都是習慣累積下來的.就像你問的這個:putting his life back together

putting XX back together = 就是把XX重新整過(再重新出發)的意思.

committed 某人 to 某事 = 為某人下定決心做某事.這裡的<某事>就是 上面的這一段話(putting XX back together)

例子:
She committed herself to the promotion of women's rights.她立志為女權奮鬥
She failed to put her life back together several times. 她浪子回頭失敗了好幾次.

Make a start again after several false starts=pulling his life back together.