first things first - tell him how you feel.
how long have you been together?
has your relationship with him been mostly a happy one, or has the relationship been difficult lately?
do you think he freaked out and ended it because of trust issues, or is it something else?
drugs (especially alcohol) can put a huge strain on a lot of people's relationships - but the fear and stigma of "drugs" for people who aren't familiar with them, or users themselves can make it hard to discuss rationally with people sometimes.
i agree with you that mdma and acid are not in the same (in terms of problematic use) to coke - especially if you've stayed away from that.
one thing i would say at this point is that if it's been an effort for you to stop using coke and drinking excessively - it's probably going to be tempting to want to drown your sorrows, but i'm sure you're aware of what a bad idea that would be.
perhaps if you give him a little time to think before speaking to him, you can reassure him that you
are in control of your substance use, because despite being sad and upset about what happened, you're still committed to keeping your life on track, and you're still committed to being with him.
to give you any more solid advice, i would need to know a bit more of the context - but either way - i hope you guys can work it out.
my substance use has challenged my relationship and made things horrible for my girl at times - but we've always managed to work things out, and we're still together after many years - i'm a really lucky person, because i've had some pretty deep lows which....yeah, worse than a bit of acid and molly without telling him.
i hope you guys can work things out, because it sounds like you really miss him.
it's bloody hard, but i think the most important thing is for you to try to repair some of the trust that he's lost in you.