I have experience. I just had the worst year of my life, I also have an 18mo. Used to post under another nn but DH came on and read everything, all my support which went down like a lead balloon.
Anyway, he had a breakdown, still has severe depression, I did speak to his GP he could do nothing but sympathise, listen to me and let me offload. Your GP can't give you a cure at the most they can tell you how available MH support eg therapy is in your area (it's shit where we are). That's it. But still go because it sounds like you need somewhere to talk.
My DH eventually went to GP but won't take the tablets. He went to therapy for a while which helped but that ran out. He seems to be getting more stable but it's been a year of destructive behaviour and me trying everything to make him well/get him help.
So from this point if experience. Just STOP. You can't help him. You can listen and reassure him you're there, you're his home but THAT'S IT.
I went down that rabbit hole and you end up destroying your own mental health and the time and wellness you need for your children. And for nothing you cannot force others to change, you can't force them to get help, you have no control. And you going down the hole will ultimately just make him worse.
I left eventually, encouraged by family and MN and DH himself. We are hopeful we will be together soon but it was the right decision at the time. Look after your family and hold the ship steady for when he is well.
The only caveat to that is if you think he reaches the stage he is a danger to himself or others, then call the police. I had to once when I believed he was suicidal
It's shit but it gets better. Hold on x