But as far as we know he MAY need to be sectioned? The OP does not know where her DH is? She just knows that he has considerable life stressors, has said he is not coping, and he has walked out.
And with respect to the rest you are just naive or blessed to have known very few people who have been as seriously mentally ill. My mother was one such person who DID just fuck off for days, leaving me even at the age of 3 in a cot in a soiled nappy alone, before pitching back up a few days later. She’d diappear for a week or so leaving my sisters and I without food, money or anyone we could contact. I know of another woman who was sectioned with puerperal depression after both her children were born, for 6m in the first instance, later diagnosed with bipolar. My uncle was someone who would disappear and reappear like this. He committed suicide in his thirties.
Look at the govt stats - there are hundreds of people who do this.
YOU cannot say whether the OPs DH is mentally ill or a just a selfish person based on the posts here - you do not have the facts. In fact I’m not sure OP does, as she is muddling through trying to raise her kids, hence PPs here suggesting she report him missing so that he can be reached and assessed.
However, if there is even a remote chance that his issue is MH related, then it is fucking important for the OP - and her children - that she considers this, gets him a welfare check and excludes it because if she doesn’t, if her actions are the final tipping point that triggers a suicide or permanent disappearance, she will have to live with the guilt and navigate that throughout the rest of her and her children’s lives. Having seen my grandmother live with that guilt in relation to my uncle, I’d not wish that on anyone, especially a woman with two teens to raise (FYI my DGM got fed up of bailing him out of the police after each episode and ignored their call one day. She never saw him again… until they visited to advise of his death and she had to identify his body.)