You've already done it! Just don't go back now.

Marijuana use is more than just illegal. Take the time to look over the whole situation. He lied to you. He can't control his habit. He enjoys his friends that support him in the habit. He doesn't see the problems.

What's in this lifestyle for you? If this is the way you want to live, and worse, the rest of your life, then return to him.

If you wish to remain true to your honorable values, and make a good life for yourself without this baggage, then just keep on walking.