My ex-partner smoked pot, and so did i before i got pregnant.
As soon as i got pregnant, i quit, and he never did. In the end, it was what drove us apart. He just sat around the house on weekends and evenings, never wanted to go out or do anything except smoke pot.

So we split up. 4 years later he quit too, and agreed that it was horrible and zapped all of his motivation and energy.