I think the OP deserves better than meaningless platitudes. Telling her she can find someone and have a baby and she's just not trying hard enough make me see red.
Life isn't fair, and a lot of us don't get the life we wanted or expected. I lost my parents young. I decided I wanted a family. I was lucky to get pregnant twice, both unplanned, and be able to support my boys. However I have no idea where DS1s dad is, and 2s dad is a total twat who put me through emotional, verbal and physical abuse. I'm in a better relationship now but due to various issues (health, bereavement, courts etc) that's not been a happy ever after.
I have friends my age (mid 40s) who are still hoping for a child because for various reasons it didn't happen for them when they were younger/ their partners weren't 'ready'. I've ended up the only person in my group with kids which is not how I thought it would go 20 odd years ago.
I think we all have regrets. There are some things we can't change and feeling sad about that is only normal.
That said I think that ultimately none of us HAS to be on their own forever if we don't want to be but it may take a lot of time and effort, and require you to do a awful lot of work to meet someone (go on 100s of dates, take up 10 different sports activities, or whatever) and even then there may be a lot of compromises too. And even if you do, children may not happen. Either or both of you could have fertility issues. It might not be something he wants (back to compromise).
I wish my life had turned out differently for different reasons. As we get to 40 and beyond we start to get a sense of perspective about time that's passed and is still to come. I think it's where the idea of a mid life crisis comes from.