Question about SOs smoke breath...

So bf and I been going strong for some 10 months now and everything is great! But my one issue is I feel less interested in really making out with him because of his breath. He enjoys a little pot now and then. He's always great about brushing his teeth and using mouthwash after but even with that it still sort of lingers in his nose and throat for a long time. Any ideas on how he could fix that?