I wouldn't describe it as horrendous but I do struggle with my eldest, and honestly it breaks my heart. He is 11.
I'm very very cheered by tales on here of DC who mellowed out by their teens! I sometimes say DS1 has been a teenager since he was 3! He really acted like it.
I have a 1yo as well and when I compare photos/journal entries of DS1 to how DS2 is now it makes me feel quite sick with sadness, I used to have this absolute adoration for him, I am certain it's a hormonal thing, I feel this way about DS2 now (this makes me feel horrifically guilty - though I am sure it's a favourite age thing, not a favourite child thing - still). I do not even like the way DS1 smells any more, which obviously isn't his fault! It's just hormonal stuff and I did read that boys develop a less attractive smell to their mothers during adolescence.
BTW this is not new since DS2 was born/conceived. It's gone on much longer than that. I can pinpoint it back to the period of him being 3-5 years old which is a time I absolutely struggled and could not cope with his behaviour. In hindsight I was absolutely insane not to seek help with it, in fact, I remember having suicidal thoughts except for the fact I would never have abandoned him to be raised by some random other person, but I kept thinking it was all my fault, and if I could just do this or do that perfectly then everything would be OK. If anything actually things have improved since his brother was born as it's helped remind me of having these intense loving/protective feelings over him when he was very tiny. He also has a diagnosis of ADHD (as do I) but he's never had any treatment or therapy or medication etc, because it's "mild" and he's intelligent enough that it doesn't look like it affects his school grades. So everyone (except me) seems to think medication is a waste of time. I'm terrified that a lack of medication is destroying his mental health/our relationship because it's causing issues that make us narked with him all the time and it's not necessarily his fault.
I can look sideways at him sometimes and identify things I really like/admire but day to day, there are so many ways we butt heads and annoy each other, and I worry about him because he seems to have no personality?? Just latches onto anything he thinks is "cool". And no drive or interest in anything other than whatever is the easiest, most low-effort thing he can possibly find. I hope to hell this is just a phase of preteenhood that they all (or plenty of DC) go through because I am so afraid that he will just slide into a route of drugs/troublemaking and I should have prevented it by somehow getting him to be more interested in other things when he was younger.
If there has been a volatile relationship with the DC's dad beware triggers of traumatic memories as well. Again not DC's fault. (This is interesting- DH - not DS1 dad - always observes that whatever happens with DS1 I'm there blaming myself/repeating it's not his fault. I do seem to have a major issue with assigning anything as being his fault. I think because I feel guilty in general about the way I feel about him, and feel that I'm wrong and that to blame him would be unforgivable. And therefore I can't assign him any part of any blame. Which is probably another story.)
Smart But Scattered is a book I'm reading at the moment which seems to help but I haven't got to the actually helpful section yet which is right at the back! It's not just for ADHD children but any child with issues where their emotional/social/practical development is out of step with their intelligence which can cause friction.
Our biggest and most recurring issue is that he is completely unable to entertain himself which means that he is either badgering for screen time (and unchecked, would be on it 12+ hours a day and would go without sleep, food and bathroom visits in order to do this - and has done all of these things) or in your personal space complaining that he is bored, and if banned from complaining will simply EXIST in this massively exhausting manner, fidgeting, making irritating sounds, winding up the baby, creating unbelievable amounts of mess, asking absolute nonsense questions, etc. And I don't understand how to ask him to not do this, without it coming out as complete and utter rejection. So we alternate between me outright rejecting him and him being understandably upset by that, or me gritting my teeth and trying to ignore the annoying stuff, which doesn't make me want to hang out with him more, and then me trying to make amends/make it very clear to him that I'm not rejecting him by actively inviting him to stuff. But you have to assemble an entire circus of delights to get him to bite, and I find that exhausting - I did not expect to be a full time entertainer to an 11 year old, in fact he needs more concentrated effort to occupy than the 1yo does, and I can't do it.
Somehow in lockdown we seem to be coexisting fairly peacefully but not without the usual issues. It's better, much much much better than it was when he was five. But I desperately want to improve my relationship with him, understand him better/connect with him, whatever it takes.
Will go back and read more posts in thread. :)