You are not unreasonable for feeling depressed about the prospect of a childless future. You had envisaged a life for yourself that included having children. So you are absolutely not unreasonable to feel depressed about that potentially not happening.
I envisaged a very different life for myself than the one I have now (different circumstances to yours) and went through a spell of depression. Counselling helped. It's incredibly helpful to be able to unload everything in a completely non judgemental space.
I think it has to be acknowledged that everyone falls into one of two categories. Those who are child free and those who have a child/children. However not everyone is in each category for the same reason so, for example, hearing from people who are child free by choice might not be as helpful as hearing from people who desperately wanted children but never got there iyswim.
OP my heart goes out to you. If you want to continue trying to have a baby then the infertility and conception boards may be of help to you. If you don't want to continue with fertility treatments (either due to finances or the sheer toll they take on couples but particularly women) then maybe the child free boards can show you the happy and full life that is achievable without children.
My best friend couldn't conceive and as her husband had an adult son they weren't eligible for IVF and couldn't afford more than one round privately. That round very sadly failed. I watched her go through invasive testing and then IVF itself. Anyone willing to go through IVF desperately wants a child. She had a spell of deep depression after that failed round. But like a PP said living life without children isn't about living an extraordinary life it's about making a life that makes you happy. She retrained as a nurse, something she would have struggled to do with children due to shift work while on placement. Her and her husband moved to a smaller house in a more upmarket area (lots of glass and shiny surfaces, it's beautiful) and bought a lovely car that wouldn't have been at all suitable for car seats. She had a lot of counselling and is now very happy with her life.
There are pluses and minuses to having children and not having children.
I'm in the position where I have children so I can see the pluses in not having children probably a little more clearly than someone who desperately wants a child. I think I have an idea what the minuses are but I'm not going to pretend I know for sure. What I do know is that there are plenty of minuses to being a parent too and that I empathise with some days being harder than others when all you can see are the minuses.
You have freedom and the ability to be selfish. You don't need far flung exotic holidays or months of travelling, you can book a last minute package deal for a week in the sun and actually enjoy it. You can pursue interest and hobbies. Honestly you can find something you are really good at, I've never found what I'm good at and probably won't have time to do that for many years by which point I'll be too old and knackered to bother. You can retrain if you want to. You and DH can spend quality time together easily. You can have a lazy Sunday with unlimited Netflix and/or reading the papers/a good book. You can go to eat in nice places that don't have to have a children's menu. You can have sex freely in any room you fancy. Essentially you aren't beholden to anyone and can do whatever makes you happy. Concerts, music festivals, theatre, shopping, road trips. Whatever floats your boat.
There is a lot of joy to be had in this world and the trick is to find the joy in the life you have not the one you want but can't attain. I wish you and everyone else on this thread the absolute best and hope nothing I've said is insensitive or hurtful, it certainly wasn't meant to be.