
I'm so sorry you're going through this, OP. It is a lot to deal with in one go. Especially when you are 23 (and I do not mean that in a patronising way at all - it would be a hell of a lot for anyone at any age to deal with, but harder when you are younger because it sounds like the first time that the bottom has fallen out of your life, so you are very much learning to write the script of how to deal with it).
The first thing to say is: I'm so sorry about your grandmother. It must be a huge shock. I am glad that you are at home with your family and able to support one another at this very difficult time. Take your time to cry, and to remember her together. It helps.
The second thing is: don't worry too much about the trailer. Work out the practicalities of what you can claim with the insurers. You may be entitled to hire another equivalent vehicle to carry on your business, you may get compensation - there are all kinds of solutions. If you don't have savings, speak to your family about a short-term loan - if they can't help, then speak to your bank about your situation. Deal with the financial stuff early and up front and problems shouldn't build up.
Thirdly: Your DP sounds like a right arse, and no mistake! Who on earth dumps someone in those circumstances? Of course, the other posters are right that you've had a lucky escape long term, but that doesn't make this any easier for you right now. My advice to you is to open up to family and friends (via internet if need be) and to cry all you want. Make sure you don't agree to anything with him regarding financial or legal circumstances without consulting a lawyer.
Finally, take your time over the future. You really can do anything, but now isn't the time to make big decisions necessarily. Be gentle with yourself, and take it easy.