Aww.. I'm so so sorry to hear that you're feeling like this.. I can't imagine how difficult it must be for you to have these feelings with your wedding so quickly approaching.
I know everyone is saying "it's stuff you can overcome" etc.. but I am going to (at least slightly) disagree.
Especially if you are a single mom.. you should be very careful.. nervousness and jitters are normal to some extent, but big worries like the ones you have, especially considering that you have a child of your own, are definitely something to consider seriously.. It's so hard being so close to the wedding, but this should be a happy time in your life.. I know nothing is completely perfect, but I don't think it's great that you have so many (and such serious) stressors.. it's a whole life that you're committing to.. if any part of you doesn't feel safe in that choice, then maybe
You deserve complete happiness.. you deserve to be happy and excited, and to feel comfortable and safe, and to some extent at least taken care of. If you believe in the two of you, and you truely think he is deep down a genuinely good person, then you might have something worth working on, but if part of you doesn't.. to the point that you're getting increasingly uncomfortable.. I think it would be dangerous for you to ignore that voice.. uncomfortable.. but a child together followed by an unhappy unreasonably stressful marriage and a potential divorce will be much worse..
No, everything is not always easy, in any relationship, but that "it" factor that NYC bride2be was talking about.. yes it's special, and important.. but it's definitely not enough..
The other thing is.. when you talk to him about your discomforts (ie.. about the wedding coming up with the ex etc..) does he seem to care? He should. And a 'good' guy would.
ALL the best to you!! I hope that in a month we will be hearing that you are happy and either seeing BEAUTIFUL pictures of your wedding OR just your vacation!! (there is no shame in telling your guests "hey, we just aren't ready" and then going on a fun vacation together!).
IF you get married, do it for you. Nobody else's opinions matter (including ours.. we aren't in your situation).
xox