My ex swanned off into the sunset when I was 7 months, leaving me with no option but to go it alone. Turns out my bubs has special needs & yes it's hard sometimes.
If I could turn back the clock would I do it again? Absolutely!!!!!!! In fact my 5 year plan concludes with long term fostering/adoption if everything goes as I'd like (never any guarantees). (My son's sen make me wary of introducing a second adult to the household, & dating is summat I don' have the opportunity to try, yet I'd love to have the chance to nurture more children.)He's taught me just how precious EVERY child is, so I'll go for older kids, perhaps those with behavioral issues if my research shows me I can handle the challenge.
As an adult you take responsiility for your OWN actions. If a partner of 10 years standing says they don't know if they want children, remember men can change their minds in their 60's and have a child with a nubile 20 somehing. Take responsibiliy, either accept a childless relationship or leave. Don't sit there winging until you are the wrong side of the hot flushes & then lose all that makes your spirit beautiful in a sea of bitterness.
Life isn't fair, never has been & never will be, some women have always been barren, abandoned, widowed, cheated on etc throughout history. Princess Diana started with the fairy tale but her story didn't end happily, others meet their soul mate at 16 and are together 60 years +. Lone parents were very common after both world wars without the state support available today, yet they coped. Very few people get the adoring hubby in the home counties, private schooling, a pony & a white picket fence.
There's a lot to be said for learning to be content with what life gives you and learning to adapt your expectations to what is actually achievable for you. If that means deciding at 40 to go it alone - go for it! You are old enough to do the sums & arrange a decent support network of friends/family etc in case you fall ill/feel overwhelmed at any time.
Do agree with what previous posters have said about men though, there's a season for everything and trying to carry on like a teenager in you late 30's/early 40's is pathetic. I'm trying to give my own son as great a childhood as I can, so that when that time passes he is able to move onto adulthood, embracing rather than cowering from the responsibilities adulthood brings. I'm also looking forward to my own "purple leggings phase" and baking my Grandkids yummy cakes ; )