I didn't think that because I had children, I would automatically get grandchildren. If I did, fine, and if I didn't, for any reason, then fine too. They are not my decision to make and not my responsibility to bring up, I've done all that and enjoyed it most of the time but it is a huge worry too, especially as a single parent.
I don't get to see my grandsons so my grandparenthood is nothing like I thought it would be when my daughter was pregnant. I was looking forward to teaching them, playing, doing craft, baking, gardening etc. All the things we love and want to pass on but alas, I haven't been able to and if I ponder on it too long then I will become upset.
When my daughter was pregnant, I thought I was going in one direction, but I wasn't, and the same is for you too, wannabe. Lots of us on here find ourselves in situations that we didn't even dream we would end up in. That's life and it sucks. But it's shoulders back, head high and move on. Focus on your own life, what you can enjoy. Book yourself a break, start a new class, learn a new skill. It's your time, for you to reward yourself for all your hard work at bringing your son up. Grab it by the tentacles and get out there and enjoy yourself. 