Adapted from a recent online discussion.
Question: My husband and I are unable to have more children due to illness. My brother's wife just had their third child. I'm happy for them but also struggling with resentment, self-pity, and sadness. I love my brother and sister-in-law, but I'm not sure why they have kids. They spend as much time away from them as possible and put them into day care the minute they're old enough. She's a stay-at-home mom, so it's not for work.
I know it's unreasonable, but I'm really struggling with "It's not fair." How do I feel good again? I know it isn't some giant conspiracy in the universe, but that's how it feels.
Answer: I'm so sorry that you're unable to have more children and that illness is the reason. Randomness like that does have a way of feeling purposeful when you're on the wrong end of it.
You do control your response to things you can't control, though, as you know. You mention your "self-pity" and that you're being "unreasonable," so clearly you're somewhat aware of your own contribution to your unhappiness.
You do your best as a parent. That's the job description. Sometimes, that means you stretch to do the best thing for your kids, and sometimes, it means you just do what you do to get through.
It's natural to turn your sadness and anger onto a nearby target like your brother and sister-in-law, but it's not the way you're going to feel better. On the contrary, it's a way of rewarding those feelings with a sense of superiority - which, of course, will ultimately feel false to you because you're just tearing somebody down.
Please instead seek remedies in the positive. Find a good, compassionate therapist, and do your talking (and raging) in the shelter of his or her office. Take faultless care of yourself through restorative means - physically if you can, and artistically or spiritually regardless. Immerse yourself in the children you have.
Your grief is clearly still raw. But that also means you have a chance to take a healthy approach to it before it hardens into something more tenacious than it needs to be. If therapy isn't an option for access reasons, try Resolve.org, because you do need to reckon honestly with the dark thoughts you're having.
Though this sounds contradictory, also look your inner finger-pointer in the eye and say, "No. I won't do that. I'm better than that." Love is your most profound ally - against injustice, anger, illness, unfairness, or just giving in to the feelings of envy and resentment we're all susceptible to.