Here is the first reason infertility sucks.
Everyone has friends. At least, I hope you do. Or at least I hope that if you don't have any, you like it that way. At any rate, let's go with the assumption that people have friends. Lovely friends. Friends in their peer group - people they met through school, through work, through other friends. People who are generally in the same age bracket with some of the same interests, although not everything because that would make it all pretty dull to hang out with a bunch of people exactly like you, because as much as you rock, 30 of you would be kind of mundane.
And the thing is, they are really not exactly like you anyway, because through some miracle, all of these friends are somehow able to have children. And even though they don't mean to, even though they swear they won't, eventually, you see your friends less and less. You simply don't fit in to their lives anymore. And soon, sooner than you think, you find yourself pretty much friendless.
It's natural. Life changes, when you have a kid. And when your friends start making all their changes with their children, you simply get left behind.
The family eats earlier, because the kid needs to eat by 6 pm to be able to go to bed by 7:30. Non-parents don't eat til later, because good lord, why wouldn't you? Dinner plans between parents and non-parents are logistically impossible.
Non-parents can go out after work for a drink, socializing with their friends. Parents have to go pick up kids at daycare. Socializing is impossible.
Non-parents don't get invited to events where kids are present, things like birthday parties or playdates (and let's be fair, playdates are just as much for the Mom/Dad as they are for the kid) because what's the point? They don't have kids, they won't want to spend their afternoon surrounded by them. Won't it just remind them of the fact that they don't have children? No, best not to invite them to the cottage/birthday party/whatever other event you're spending with other Grownups With Kids.
And besides, you're not an ideal companion anymore anyway. You're missing a "part". You don't have a kid for their kid to play with, so that automatically makes you less fun, less desirable as a weekend companion.
I could go on, but you get the point. I am also not crazy about the idea of listing the many ways in which we've been neglected, because despite the fact that this is my blog, I don't want to spend the entire time whining. I don't begrudge parents their children; I do understand why they've made the changes in their lives that are resulting in me seeing my friends less and less and less.
I'm just trying to tell you something here, that when you're trying to understand what it's like for people who want kids and can't have them, the pain isn't just the empty spare room. It isn't just having to duck your head and scurry by the cute kid's clothes that you'd love to be buying when you're out shopping. It's the fact that everyone around you is moving on to the next phase of their lives, the parent phase, and you are unintentionally but inexorably left behind. You've been with your friends for years, through the thick and the thin, through the school and the job and the bad boyfriends and the good boyfriend and the wedding and the crazy parents. And this is the first time your friends are doing something that you are not, that you want to do but you cannot. You are solely and uniquely left behind.
And it sucks.