OP I'm sorry you're going through such a difficult patch. I only had one DC and I found the baby and toddler years really difficult. Hats off to you (and all the other mothers) juggling multiple small children.
Based on your initial post only, your DH hasn't committed any major crimes. He found your missing scarf, but in the process, he dumped a load of bags in the hall. He took your DS out on an errand, but stopped off at the park for about 45 minutes without telling you.
However, from reading your subsequent posts, it appears that these acts are the latest in a long line of incidents where you feel your husband isn't behaving like a team player and isn't communicating well with you. You're very tired and stressed and his actions are making things worse for you, not better. So in the first example, he picked up on an idle comment about a scarf. While he found your scarf, it wasn't a priority for you at that time and he's left a mess for you to clear up. In the second example, he popped out on a brief errand. But instead of coming straight back like you expected, he delayed coming back. Ok, so you could have texted to check where he was, but you didn't know how long he was going to be at that point. And anyway, why should you have to text your husband to find out where he is? A quick text from him along the lines of, "I was going to stop off at the park with DS. Is that ok with you?", would have given you the option of saying, "Yeah, that's ok", or, "Actually, I'm finding DD really hard work today. Would you mind coming straight back". Instead you were left staring at the clock and (no doubt) thinking, "Where the fuck is he now?" and getting more and more frustrated.
It sounds like you're at breaking point and you're harbouring major resentment about your DH and how his life is still the same, and he just comes and goes as he pleases, while yours is so difficult and you're so tied to the DC. If this carries on, that resentment will lead to divorce.
I would really recommend the following
A day away from the DC, to get a break and a bit of perspective. Or even better, a good night's sleep. And repeat this at regular intervals. I get that your DC are very needy right now, but you know that saying about how you can't pour from an empty cup. You'll be a much happier mother if your needs are being met and you'll be better able to cope with the demands of your DC.
A session (or multiple sessions) with a counsellor, to tease out all of this. A good counsellor will help you to work out why your DH's behaviour bothers you so much and could help to come up with some suggestions in terms of how to broach the subject with him, so he really takes in what you're saying, instead of brushing it off. Also, you're carrying a mix of resentment, anger, stress etc. and that's a very toxic mix. Better to release those emotions in a safe environment.
Could you afford to employ a cleaner? I know that's a bit of an MN cliché but your very first post said that your house is a mess. It would be one less source of stress.
Forget about the toilet training for now. You can try again in a month or two. You've too much going on right now.
The bags in the hall are not a priority. Get your DH to sling them back under the stairs and you (or even better, he) can tackle them at a later stage.
It's hard to see it when you're at the coalface of parenting but these tough months and years won't last forever. One day you'll find yourself with a self-sufficient young adult (or in your case, adults) and the times you're living through now will be a distant memory.
Do you have any family or friends nearby who could help? If I lived near you, I'd happily pop in for an hour or two and hold/walk the baby, so you could nap or head out for a coffee or whatever. It's a pity there isn't some kind of befriending service whereby older mothers like me could give a hand to frazzled young mothers. With sympathy and zero judgement.