Jelly I am so sorry that you are going through this. You must feel as if you've just been run over and that your future has just gone down the drain.
Well, one future may have disappeared but that doesn't mean that you won't, one day, have an even better future - one based on total trust, honesty and respect. No one can tell you when that's going to happen but it will, and you will be thankful that you had such a narrow escape.
I don't mean to sound flippant by writing that .... I know you must feel unimaginably terrible right at the moment, and be hugely worried about what's going to happen in the next few weeks.
Right, you need to call a trusted friend or relative (or more than one) and tell them what's happened. You will almost certainly find that they will bend over backwards to try and support you through this, be it taking charge of the practical things that now have to be sorted, be it calling round all your guests, or even by taking DS off your hands. Please do this - you have nothing whatsoever to be ashamed of and by getting other people involved, it will help (in a tiny way, but better than nothing) you to start to deal with what's happened.
Again, I am so so sorry ............ your ex is obviously a very immature coward, despite being 36 and, in theory, "old enough" to "know better". There are decent honest men out there and one day when you are ready, you will meet one and this will feel like a bad dream which happened to someone else.
Big hugs.