Newbie, but really struggling

Hello, don't really know what I'm hoping to get out of this,  I think it's more of a hope that somebody can at least identify. 

I'm a 41 year old dad and have just had my autism assessment (waiting on the results) but I struggle sooooooooo much being a dad.

I just can't be the dad I want to be, and kills me so much, and it seems like my issues with sound and my need for timeout is effecting my daughter. I feel absolutely awful. The noise just gets too much, the lights everything and then I end up get snappy and being all moody n stuff, which obviously my daughter is witnessing. I've explained to her that's she's a good girl, she's done nothing wrong, and that daddy's got a few issues he's trying to deal with and that she's done nothing wrong, I've even tried to explain to her that it's like a volcano, the pressure builds. When it gets too much, I do end up s/h.

My partner is the one who takes her to the parties, all the social things cause I am awful with it. I even get anxious taking her to the park. I have missed out on a lot because of the issues I've got, but more importantly, she's missing out on time with me, and it breaks my heart. 

It's causing issues with my partner, which only adds to the stress because I'm worried ill lose them, and it's like a never ending loop of stress. I'm hoping, I'm praying I am diagnosed, so I can get the help I need, and be able to explain to her in a more accurate way why I am the way I am.

I'm not after sympathy, I'm just hoping someone else might understand, cause honestly I feel so alone with this, and I often feel they'll be better off without me.

Thanks if you've managed to read this.