Hi, well "-aba" just means past tense. things that use to happen, and not just once. hablaba - spoke, sentaba - sat, comenzaba - began. Like: (once doesnt need to be said, but it is understood) Él vio al hombre que ayudo antes =he saw the man who helped (once) before. Él vio al hombre que le ayudo antes =he saw the man who helped him (once) before so the sentences change depending on who or what happened. for ex. Él vio al hombre que ayudaba antes =he saw the man who helped before. Él vio al hombre que ÉL ayudaba antes =he saw the man who HE helped before Él vio al hombre que le ayudaba antes =he saw the man who helped him before hope it made some sense hehe =)

Ambas frases son correctas. La segunda frase tiene un complemento indirecto "le", lo que significa que vió al hombre que le ayudaba a él. Yo, él, usted, son pronombres personales, e indican distintas personas cada uno.

Both of them are correct, just that changes the meaning of who was helping to.