Relapse is shit. There's no way to avoid it. No matter how much you dress it up as being 'part of the journey' (which it still is), it's undeniably shit. For me, relapse is always filled with terrifying 'what-ifs': what if this is the relapse that takes me back to how I used to be? What if I'm getting bad again? What if this isn't 'just' another relapse?
And for me, that's never gone away. I'm lucky enough, and proud to say that I've been relapse free for over a year now. But am I still hella scared of relapse? For sure. Each relapse led me into a pit of terror of thinking that I would never recover, that I was getting dragged back into routinely self-harming, and that maybe (just maybe) this time I wouldn't have the strength to get myself out of it. I've spoken more in detail about being a 'recovered' self harmer, and the stigma that goes with it, so I'm just going to say here that being 'recovered' doesn't mean you necessarily feel free from the thoughts of self-harming again.
The thing that really sucks is that relapse happens. No matter how much you put your mind to it, and no matter how strong you are, you won't just wake up one morning and be self-harm free. I always think of self-harm as an addiction, and like any addict, going cold turkey is tough and there will always be slip-ups. It's a really bitter pill to swallow I know, but knowing that you're not alone on the relapse front is something that can genuinely help. It's normal to struggle and to want to relapse and to be scared of relapsing, and accepting that it has happened does not mean that you've been defeated.
I found the post-relapse guilt the hardest part to handle. Guilt turns into anger and anger into self-loathing, and that had the potential to send me into a whirlwind of more relapses. I think to some extent you'll always feel guilty for relapsing, especially if you've got people helping you along the road to recovery. It sucks to have to admit that you've relapsed, but it is not a failure. It never will be: it's all a part of recovery. And yes, there might be times when the relapse isn't just one occasion; when it goes on for a week or a month, but even if it does, it does not mean it won't end. You will recover, and it will take time, and there will be relapses, but it will be worth it.
I'm by no means some kind of 'expert' on the topic, but I know what helped me. It helped to remember that no matter how many times you relapse, you are not letting anyone down, even if they say you are and don't understand what's going on. Relapse will happen when you're trying to recover, and it's okay. Accepting that it's happened rather than trying to ignore it, or going over and over it in your head is always going to help. And yes, accepting it is hard, and it's normal to feel guilty and angry at yourself for the relapse. All those feelings are fine. They don't make you any less in recovery, and every recovery from a relapse is one step forward.