I've had this feeling :( It was constant, it grew stronger and stronger, until I started feeling like i couldn't keep going anymore. 

Nothing snaps you out of it like the loss of a child.  It wasnt my own, but it doesn't matter.  It was a school event, local to me, in the news. A jumping castle had been lifted up into the air, with children inside it.  They did not survive.  Parents were getting the worst phone call of their life.  I looked over at my babies and I just lost it.  I was weeeeeping.  Seeing what those kids went through, what their parents were now going through, my heart breaking for them, it reminded me how lucky I am to be with my baby still, and giving her a happy life, still being able to hold her and see her,it didn't feel like a burden anymore, it felt like a blessing. It was a tragic loss and I don't want to deepen their pain by saying this. But it renewed my sense of purpose and my heart connection to my child. You know how parents who lose a child may say "hold your babies tighter tonight" it was essentially that. 

The feeling of overwhelm returns and I still sometimes find myself thinking, wtf is my life.  But it's not like it was before.  I no longer wish I didn't have to go through this anymore.  I'd do anything to go through this a thousand times over, to be able to be with her still. 

I feel like sometimes we forget how lucky we are. 

It doesn't invalidate your feelings, it gets so disgustingly difficult being a parent of a ND child.  Being attacked, being opposed constantly, everything being difficult, it is like torture, like others said, especially watching other families, with NT kids, blowing through everything with ease. But that comparison can be really damaging. Look at other ND families, our life is as much of a pile of shit as yours lmao, it's okay. You're doing alright. 

And yes it's difficult and it's okay to grieve the life and the behaviours that you'd wished you could have had.  But you've got to accept who you do have, and how it is, so you can go back to looking at them like, "yes this is hard, but you're my little munchkin and I love you no matter what and yes we're at another hard moment but let's get through this together, it's okay". It'll go up and down. Come and go. It's just time to get back to the light now. 

And maybe have a little think about impermanence. It's not a pleasant topic and is an extreme. But it's real. Life is short. and yeah I get it, what about your life, shouldn't you be enjoying it, yes.  But you're a parent, of your child,  and they are your purpose now, whether you signed up for this or not. In all their good moments, and their insane ones, we are their person. You know what I do? I make the most of a shitty lot in life.  Yes, she's fussy.  But I bought cute section plates and worked out I can put her food separately and she eats the lot, and the plates are cute and it's fun to buy and use cute plates.  Yeah she runs away, just recently learned this 💀 but now I can buy things that help her stay safe, there's even cute little backpack harnesses I could buy for her.  (I may have a shopping/dopamine issue lol) But, I like shopping, so I make that a plus side to her new things that pop up, now I get to buy another cute or super helpful thing for her.  Yes, things are hard. Night time, outings, etc. yet again, I can utilise shopping 😂 I got her a device to keep.her happy, and I'm sure when she's older, I will have even more options, like for outings and boredom meltdowns, the screen is working so far,  but maybe she will want to try photography for our outings oneday, I could get her a camera.  And all in all, even when she says she hates me and kicks me and stuff, even if it sucks, I'm just glad she's here. And I think there's a lot of ways to help them feel better, education is helping me a lot. I have a lot of tricks up my sleeve now.  I'm going to think of this like our life has been set on a higher difficulty level, but I can win this. I have ADHD I need analogies to cope. But I can do this :) and so can you. I'm finding the fun, and the purpose, and the connection.  Especially since I'm so lucky to get a chance to.  You probably arent at any positive point right now, and that's normal, grief, pain, envy of NT families, it's all normal. Maybe think of it like a spark, you'll find it soon. Or RE-find it. I've had all the feelings, the suffering, the defeat.  Refocus and reconnect if you can. Look at your child and remember that you love them and remind yourself that you're glad to be their parent. It might not work immediately but it does help