This sounds tough OP. It sounds like you've got the important stuff gripped already; understanding this is likely to reflect limitations in his developmental capacity, so he is not intentionally being naughty, and one of the few variables you have to play with are your own expectations and reactions.
Can you make life any easier for yourself by doing less on any front? Stay in more if the transitions out are hard? Order online and avoid shops etc?
Can you join a local support group with mothers facing similar challenges - this can be such a relief, plus you pick up local tips on support services etc?
Can you prioritise doing a bit of the things you both enjoy together, every single day, in order to consciously invest in your relationship?
Can you keep a little notebook observing small but lovely moments, to remember, as it is so easy to be completely overrun with the difficult stuff.
Have you got some activities in your life that you enjoy and can be absorbed by if only for short periods every day?
Can you confide in friends - so you at least feel heard?
Has DC been referred for an autism assessment?
Does he go to nursery yet - if so, are you getting any support from there? Have they suggested applying for an EHCP (if you are in England?) or does he have one already?
Not sure if you can keep records of the trickiest situations at home and what leads up to them to see if you can spot any patterns in what is happening in the environment around DC, or what sort of demands may be being made on him, that he can't cope with?
Professionals usually advise treating children as though they were considerably younger, to reflect differences in development?
Scope offer a mentoring service to parents in the year following diagnosis.
Local neurodisability services or CAMHS may have a number of practical videos for parents on their website.
Sorry - that's a bit random. Other people will have better ideas.
Good luck