This one is for me.
Jess-
I know I'm hard on you. I expect so much, push so hard, and don't take enough time to give you rest, to be gentle with you.
So here it is.
You were/are completely valid in your decision to end things with Jason. You knew deep down that you couldn't marry him, that because of his bipolar (and because of things outside his bipolar as well) there were fundamental deal breakers, things that couldn't - that still can't - be bridged, fixed, or changed.
You were justified in staying though. You love(d?) him and that doesn't just go away. It shows the depth of your feelings and commitment that you stayed so long and tried so hard to make it work. That doesn't make you weak. It makes you human.
It's okay to be unsure and feel conflicted. It doesn't mean you made the wrong decision. It's okay to feel angry with him and still miss him. Those aren't mutually exclusive. It's even okay that you feel like part of it is your fault, but just because you feel it doesn't make it true.
So take your time. Be unsure and conflicted. Ride these emotions out. Because they will subside. You won't feel this way forever and thank goodness for that.
You've gotten through tough breakups before and you've had a lot of time to prepare for this one. Deep down, just like you know you can't marry him, you know you'll be okay at the end of this.
And just think what could be waiting on the other side of "okay."
Please be strong, be brave, and please be gentle with yourself, Jess.
And know that I love you.