Jodie, these are words. He wants to get clean. His actions must follow and be consistent for a long time, otherwise it's just the same old roller coaster until he does.
When there is active addiction, there is no logic. Why he left you or why you left him doesn't matter. In the end, his choice was drugs, even though with that comes guilt and remorse.
Personally, I wouldn't put too much importance on what he says here. He's sad and he's sorry...and he's not clean yet. At this early phase, it's still just a "pause". Real clean and sober comes with time, a lot of time and work.
I'm sorry this throws you, maybe take some space for yourself today and find your balance again.
Hugs