Many people think that their activities in Facebook are only seen by themselves and those images and things he shared will be available to others, but this is a misconception because when you like or comment on a picture or post your friends will know about it.
If your LCD or screen of PC is large enough then you can see that on the upper right side of your screen there is a live feed going on telling you what your friends are doing on Facebook, if you are not seeing it then reduce the text by pressing ‘control and minus(-)’.
There is another technique know what your friend is doing on Facebook. Just write ‘Photos liked by XYZ’ write your friend’s name instead of XYZ and then click the search icon, Facebook will show you pictures which were liked by your friend in past.
By writing Posts shared by XYZ you can see the posts which were shared by your friends, so try it and know what your friend have been in past months.