Welcome to the club no one wanted to join. You will find many here with great advice.
As far as not being married - Um you are as close to married as you can be.
It doesn't really matter, you obviously were both in a commited relationship.
So his A was 2 year on and off thing? How long have you been looking to leave? Was it prior to that? If so were you feeling the disconnect prior to that? If you were I would push for more info from him....Just saying cheaters minimize, especially when they think we don't have proof.
Read in the healing library up on the left side of your screen there is a ton of useful information on how to start healing, and move forward from this point.
You should probably do a few things to help protect yourself, and start healing yourself.
1. See a lawyer, find out what your rights are and what would happen should the relationship dissolve. Knowledge is power, and power gives you strength.
2. See your Dr. get STD tested, yes YUCK but it is the harsh reality of it. IN addition if you are having trouble with sleep, eating and staying hydrated talk to the Dr about it, and see if you need a little pharmaceutical support (ie, antidepressants, or antianxiety meds) to help you through it.
3. Tell yourself everyday, and multiple times a day that his choices to do this had absolutely nothing to do with you. He is 100% responsible for his actions, and neeeds to own that.
4. Take time to figure out what YOU want. If you want to try to R. What are your conditions, get that stuff figured out. So that when you start therapy, you can tell him what it is going to take to make you feel safe.
Choosing not to stay is ok too. He never made you feel safe enough to say I do. Why? Perhaps individual counseling will help you to understand that with yourself.
keep coming here, and posting, we care, and many of us have BTDT.