Hi angharad. The grieving/mourning feeling does take a good while to ease. I found I was still grieving/mourning my old 'friend' for a good 5 months. Obviously peaking in intensity for week long periods or so.
I still get pangs of grieving/mourning hit me at times. It's only natural especially at 24 I reckon. But I know I am doing the right thing and the good that sobriety brings vastly outweighs any drinking/drug binge. I can't believe how I was willing to put myself through such a rough time mentally/physically just to hit a brief couple of hours max of plateau/high.
just thinking of some of my comedowns/hangovers from booze and drug cocktails makes me get a small panic attack! lol.
Mourning and grieving is all part of the process. Accept it and you'll be OK.