How do I tell my boyfriend his breath stinks ?

Back when we started dating two months ago, it was fine, I liked kissing him. But recently, I’ve noticed that he has a stinky breath. I’ve been avoiding kissing him because I can’t stand it but he’s getting suspicious. He’s complaining that I don’t kiss him as passionately as I used to, sometimes I don’t kiss him at all. When I really have to, I hold my breathe.

How do I tell him that the reason why I don’t kiss him is because his breath stinks?