Best of luck to you Sarah. I can relate to your fears after being badly hurt myself in the past by a cheating first wife.
I had to learn to trust again.
I decided i would stay single forever so that i never got hurt again. I had no kids, but 2 beautiful neices, and one buff head nephew!! (in a kind way!!lol).
But then after i settled down and started thinking properly, and positively again, i thought to myself that true love really is a beautiful thing, and something that i didnt want to deny myself of for the rest of my life. In a way that would be like spending the rest of my life suffering from the actions of my 1st wife.
So i moved on, got a girlfriend that lasted 6 months but didnt work, then single again!!lol
Then at the age of 30 i started dating my current wife. I have 100% trust and confidence in my wife, and although we argue occassionaly, i love her to death. I had 100% trust in my 1st wife too. I had the "it'l never happen to me" attitude.....boy was i wrong!!
Obviously i have learnt to trust again which was a major hurdle for me.
Unlike yourself though, once me and my wife hooked up, i piled on over 30kg!!lol
Honeymoon is over now and im trying to drop it!!!
Good luck with whatever the future holds for you, and keep your chin up. It takes courage and risk to get the best out of life.