I'm having anxiety about my new relationship! please help me.

I've recently started dating A guy I met when I was 14. Long story short he lived in a different state so life happened and we lost touch. We finally reconnected and he dropped everything and moved with me in the state I live in. He has 2 kids and I have 1 which is fine I accept them as my own. Everything is wonderful he is perfect in every way but I have anxiety because of past relationships, I'm afraid that everything will fall apart then I'll be left heart broken again. Like I am currently up at 3:27am thinking of everything that could possibly go wrong. I was single for 3 almost 4 years before him.. I've tried working towards relationships with ppl but it's always been awful now I'm afraid like I'm literally awake crying. What do I do? SORRY ITS SO LONG!