Your DH needs a therapist. He sits around in the evenings pining away for his ADULT children? When my minor skid was totally refusing all contact with DH, he didn't do that.

Go out and find something fun for YOU to do, and leave him behind.

My DH pines now and then too, but nothing like it was. Like Evil3, I just decided to do my own thing. No need to go down the rat hole with him. He could be miserable if he wanted to, but I have a life and it's not my job to make him happy. He didn't like it, but oh well.

At a very low point in our marriage, I insisted that DH get some therapy or I was out. It wasn't just about kids, but partly. That was maybe three years ago and he still goes for "tune ups" now and then. He has turned his life around and is a much better partner and happier man.

There are occassional regressions, especially around the holidays, but we deal with them. Worst part of it now is that when I come home from work he thinks I'm going to be excited about the latest antics of his kids and grandkids. I have perfected the response: "Mmmm hmmm, I'm glad they're well. What should we make for dinner?"

Understand that this is HIS problem that you can't fix. Take care of yourself and your own happiness.

My SO has slid down into the "mopes" with regularity and it's not easy.  Nor do I think it is easily fixed.

He has reached a stage of life where he is terrified to fully retire because he has "nothing" else.  (I guess he considers his life with me "nothing") 

He despairs because he has no friends (he makes no effort to make them).

He despairs because he is bored (yet he refuses to do activities he used to like and has equipment for - boating, biking, etc.)

He despairs because he has no meaningful relationship with SD (yet he helped raise her to be a self-absorbed princess like her mother, who has absolutely NO REGARD or interest in him nor his entire extended family)

He despairs because he is afraid he will have no purpose (yet he refuses to do volunteer work or join civic groups)

Quite frankly, I'm tired of it.  I know it isn't all step-related, and this is just a phase of life for many people (mostly men) but I will be damned if I will keep trying to emotionally pat him on the head while he mopes around.  F-it.

I am going to continue doing what I enjoy.  If it gets to the stage where his mood appears to be permanent, then I will be considering moving on.  If he acted like this when I first met him, I never would have seriously dated him.  Way too negative and crabby. 

He does this every day? There’s something wrong with him, I suggest counselling. Or a boot up the ass. Stop trying to fix his boo boos, all you’re teaching him is his behaviour is normal & it’s your job to make it all better. It’s not. He’s a grown assed man who needs to sort his sh*t out.