Are friends with benefits supposed to cuddle?

There are after-sex activities other than one of you putting on your clothes and then leaving. Nothing is no more of an obvious sign that you are crossing the line in a FWB relationship than cuddling after sex. This is a big no-no and you must know that you cant do this in an FWB relationship.

Can friends with benefits be affectionate?

In friendship with benefits, the friendship and the benefits are typically non-exclusive, recurring sexual (or near-sexual) activities. Sex between friends with benefits is more recurring and affectionate than that of a one-night stand, although the sex is not part of romantic love.