Both cases are correct. But they have different meaning.
To help + infinitive:
- I help Mary to do her homework (to assist)
To help (negative/interrogative) + ING:
- I can't help falling in love with you (to avoid)
Let's listen to an Elvis Presley song, performed by UB 40: "I can't help falling in love with you"
"Wise men say - Only fools rush in,
But I can't help falling in love with you
Shall I stay - Would it be a sin,
If I can't help falling in love with you.
As a river flows
Gently to the sea
Darling so it goes
Some things are meant to be
Take my hand - Take my whole life too,
For I can't help falling in love with you.
As a river flows
Gently to the sea
Darling so it goes
Some things are meant to be
Take my hand - Take my whole life too,
For I can't help falling in love with you.
For I can't help falling in love with you"