It takes time. I know that sounds like a really lame consolation, but it's true.
He was your first love and you haven't really known any adult life without him in it. Him leaving is not the sort of thing you can "get over" in a few months; in fact a couple of years might be more realistic given your age and the timescale involved.
You may find counselling helps as it will help you examine why your life feels so bound up with your X's presence and therefore reveal ways you can disengage from him and move on to build a happier, single life. If you feel very low about it all, I'd really recommend this.
Alternatively, all you can do is wait it out and do your best to build that life anyway. Make new friends or grow the friendships you already have. Take up a new and exciting/absorbing hobby. Get together with other single parents (makes you feel less different and tends to offer much more in the way of social and babysitting opportunities), throw yourself into work... all those things will help, and the more of them you do that your X has never had any association with, the 'freer' you will feel and the more you will have moved on.
You may or may not meet someone else. No one can say. Successful relationship involve an awful lot of luck, although as you have to be 'out there' to meet someone, the more you build your life, the more chance you have of meeting someone who shares your outlook and goals. But I wouldn't recommend dating for now, until you feel you're over your X sufficiently.
As for DS, don't worry about it. Most single mothers I know (including myself) had this concern. It's natural and shows you are a good mum who will consider the effect of her relationships on her child. If you feel ready to date, and you meet someone who you like enough to have a meaningful and happy relationship with, you will find that by the time your relationship has progressed to a stage where it's appropriate to introduce DS, you will see it as life enhancing for you all, rather than a heart-sinking responsibility that has to be endured.
Hang on in there. It does get better. 