6yo behaviour

Hi ladies,
I am at my wits end with my 6 year old son. I don't even know where to start so I'm going to just blurt out.

He's always been a difficult child, from the day he was born. He spent most of his babyhood crying and being miserable which I thought was due to reflux. The doctors generally brushed me off because "babies cry" but i felt it was always more than that. Toddlerhood was not much better, constant tantrums and general unhappiness. Whatever, toddlers are supposed to be difficult right?
As time has gone on, he has just got worse. I can't take him out anywhere because my anxiety has reached an all time high. He is rude, disrespectful and just does not care what any one says. He does what he likes when he likes, says what he wants. I don't know if 6 year olds know how to maniplulate but it sure seems he knows how to. If he wants to do something and we say no, he will scream, throw things and say horrible hateful things and it will go on for hours. Every single room in our house has a hole in it from him either slamming a door too hard or throwing something. I end up in tears daily because I just don't know what to do any more. From the moment he gets up it's arguments (it could be about anything, from me getting the wrong socks) and when he gets home from school it starts again and it's over anything and everything. He will threaten to kill himself over the smallest problems. He is very destructive so toys are very few and far between because he just breaks them. He will draw on literally anything. Sometimes he will say he's sorry by writing on his bedroom wall "love you mummy" in permanent marker (we always think we've got rid of them all but he will always find one we've missed). I'm so mentally and physically exhausted and it's affecting the whole house. His poor dad gets home from work and has to deal with me, our untidy house, tantrums from the 6 year old. His older brother wants nothing to do with him because oh his behaviour. I feel so sad and defeated right now. I love him so much and he can have moments where he melts my heart but generally this house hold is pretty miserable and I'm not saying Im not to blame for how he has turned out because I have said and done things out of pure frustration I'm not proud of but I never thought it would be this hard. I keep telling myself tomorrow is a new day and then tomorrow comes and Its the same bullshit as the day before. Im in the process of getting help for myself but as someone who suffers depression and extreme anxiety, it's taken a long time and Ive done so much more damage to my own mental health for taking so long. I need to get him to a doctor but trying to get a child who will do nothing unless he wants to is not easy, especially if it results in another outburst. I don't know what to do, Im just so done.