My boyfriend loves me a lot, but he started smoking. He left me up saying that he don't want to destroy my life but I really love him and I can't leave him. PLEASE HELP ME!!

Smokes what? You say you can't leave him, but he left you.
How old are the two of you?
You can't stop him from smoking. That is something he has to want to do.

If he doesn't want to change, either you accept what he does or break up. If a man says he will not stop - he means it.

He did not leave you because of smoking, unless you told him to leave. If he left you, there are other reasons.

You can not make him stop. This is his choice alone.

If he can leave you so easily, better find out now, and of course you can live without him.
In fact, if you ever believe you cannot live without someone, you need to consider, since we all need our own lives.

He just started smoking and he is already so addicted that he has to give you up instead of the tobacco (or whatever he smokes)? That's pretty far-fetched.
But, if he is determined to smoke and you are against it, and considering the eventual problems the smoking will cause, let him go.