There are two main kinds of morpheme: bound and unbound. A free morpheme is also called unbound morpheme. It’s composed of words that can stand alone. These words can appear as lexeme. A bound morpheme on the other hand is a mere grammatical unit which doesn’t occur by itself. It always needs to be attached to a free morpheme.
Thus, the free morpheme here is “help”. It can stand along and serves as a lexeme. The affixes “un” and “ful” on the other hand are examples of bound morpheme which are naturally dependent.