It does get easier as they get older.
Even just nipping to the shops is much easier when you don’t have to drag your kids out with you.
You can actually sit down with a coffee and a game on your phone, without them almost killing themselves like when they were toddlers.
It does make me sad that you are basing your happiness on having a relationship.
Apart from sex you can still have meaningful relationships with people that don’t have to be partners.
Your biggest issue here is WFH.
I would literally be tearing my hair out if I WFH.
My career is literally a huge part of my life. I am needed in my job and it’s rewarding. Even the times when it’s stressful I thrive on it.
I am exhausted from the socialising I do from my work that I don’t have time to be lonely.
Then on the weekends I get to have fun with my DC, going for walks, playing games, going swimming etc.
Don’t get me wrong I completely understand how hard it is.
I got pregnant as a teen and my mum kicked me out so I was homeless. I had zero support from the dad or his family and zero support from my family. As my friends were all so young they left me too and any parents I met through nursery and school etc were much older than me.
When I got my first home for months all I had was a mattress on the floor that me and my DD shared and a kettle for her bottles, no tv, washing machine, fridge, sofa etc. But I was so thankful that I had a safe place to call our own.
I had awful PND and I would go weeks without seeing anyone. But every day would get a little better because my DD got older and I got things like a TV etc.
The biggest thing was that I went from being an evening cleaner (so I could take her with me) and didn’t see anyone, to getting a job that I saw people and I was valued and respected.
I wasn’t just a mum, I was my own person.
If you don’t want to stop WFH then find other ways to get meaning in your life.
You need to socialise more (even if it’s not with friends) and find a hobby or something.
I live rurally so it can be difficult but even a weekly book club might be of interest to you.
If it’s local then leave your eldest in charge for an hour.