Arguing about smoking

My boyfriend smokes weed "every once in a while" and thinks it's fine, no big deal. It's how he relaxes or so he says. I was raised by two police officers and am 100% against it. We've been together for 5 and half years now and it's something that we argue about on a regular basis. He always tells me that my reasons for him not smoking are not valid. That I don't have a good enough reason, my main reason is that I don't like it. And that alone should be enough for him to stop. He told me that he will never stop smoking. Even if I left him. How I can I have kids with this man? How can I trust that he won't do that around my children?

I tell him I would do anything for him and that I love him more than anything. He says it back but that's obviously not true.

How do I "get over it" or how do I make him understand how I feel? HELP!!!