Hola Michael

I think you may be confusing the gerund with the infinitive. In Spanish we always use the infinitive (-ar, -er, -ir form, e.g. fumar, beber...) - Our gerund (or present participle) form in Spanish would be ending in -ando / -iendo. So, what you don't find in Spanish is:

He dejado de fumando (I have stopped smoking)

Ella dejó de bebiendo (She stopped drinking)

I hope this clarified it.

Saludos