Gonna go out on a limb here with my personal analysis....
Your brother is a pussy whipped cuck with no, what we call here in Texas, "Scene Control". Sorry you had to deal with the brunt of that. Hopefully he'll realize the situation and sack up and get some things rectified.
For my chip in on this thread; both my wife and I have been managing , in our own ways, through what happens every holiday season. We're childless (not for lack of over 15 years of trying). And it's the big hole we both have in our lives we can't properly fill. Normally we host X-mas here at our house, and this year we didn't. So her brother hosted at his place. He has a great wife, and she has a big family too. Between them they have 5 kids (three his, two hers, all now 17+ years old), and two grandkids (one that's 5 now, and one that turned 1 yesterday). She handles things by just not being big on kid engagement, focused on being around her parents, her other brother, and the adults. My problem is I love kids. Their 5 year old granddaughter and I get along and she wanted to show me things she'd made. The infant though my beard was just the most fascinating thing in the world I so played with her a while. Watched my brother in law having an absolute glowing time being "papa" and carrying the baby around. And I thoroughly enjoy spending all the time around them.
Then I get away from there and it's like coming off a heroin binge. I realize I'll never get a father's day card, I'll never teach my kid how to work on cars like my grandfather did for me, I'll never walk a daughter down the aisle, Or share a first beer with my son. When my wife and I are old we'll have nobody to care or look after us other than each other. And it's a hollowing pain, my throats tightening up just typing about it now. This fucking sucks, and it's just a cycle I know I will go through every time I'm around a lot of family. Makes me almost happy in some ways that all the parts of my family where there are kids (my nephews both have packs of kids) are in other states. When I was younger, I used to have dreams where I had kids... Since we realized the finality of our fertility failures even those have vanished.
And I can't imagine wanting to take anti-depressants, as I don't see how drugging past it would make things better. And the closest I have to compensating for it is the stupid degree to which I over-treat our pets like they were our kids....