His ex.

Recently my boyfriend of almost 5 years brought home some stuff that was left at his parents and in that stuff was his exs underwear, he made a few jokes about it. Then I said 'I sure hope you're gonna throw those away' to which I was met with silence and then found out he didnt get rid of them... now hes being extra loving lately to make up for it. I dont understand why he wont just throw them away! Why keep them?