Her Ex has, is, and will experience the same crap you went through. Then she might show up with you again, albiet temporarily.
Your questions are still fueled by ego.
"Why does EX get what I can't have"
"shes out living this awesome life now with no remorse. Like I was nothing."
Your grieving what you lost. The time you put into this.
I get it, 8 months ago I was engaged. 6 months ago I slept my first night In a camper (as i have done for the last 6 months) and had to rapdily pull my 8 year old son out of school, 3 weeks into a new school year, and put him in a new one.

It's easy to be angry about what you lost, or what someone else is "enjoying" in your stead.
Stop tying your happiness to her.
You were happy and content before you knew she existed, and you will be so again.
Women like this are The Moon, they shine only based on the reflected light of the Sun. They themselves have no illumintory power. The Moon is ever changing, mobile, and often absent.
You are The Sun, you generate your own light and heat, and The Moon needed it while in view. Now its your new moon, she is gone.
Its up to you what you'll do when she Waxes again, for as sure as The Moon shall rise, she will.

Both.

So what about her ex huh? I think they dated for around a year. They had a dog together. She thinks she can be truly happy in the mountains. Part of me believes her, at least it would help. Im just having such a hard time trying to understand if she has BPD or if she was just using me as a emotional support animal.

Thanks for the thoughts.  I definitely had in my mind not to forget that he is only 5.  Kids can say the silliest things sometimes.  My wife often will have her rants to me in front of them and she has said in front of them numerous times that she just wants to go find someone else she can marry that will treat her the way she deserves to be treated.  I'm sure he's heard it and picked up on it.  I was afraid that once he couldn't find her he just assumed she had left to do just that.  It worries me a little.  I'm just afraid he'll develop the same fear of abandonment from hearing her talk about finding someone else and thinking that means she is leaving him also instead of just leaving me

Kids can and will say some crazy things with their imaginations, so I wouldn't read too much into it.  Also remember that they have no filters so what they think comes out.  I'll share a quick story of my BPD kid though to put you a little at ease.

My two girls were 6 and 8 in elementary school.  A very large 10 year old girl was picking on all the kindergarteners one by one in an after school program (Boys & Girls Club).  I can't remember exactly what she was doing, but it was typical bully stuff.  And this girl saw that my youngest had just got a snack from a teacher, so she went over to take it.  My six year old protested and said it was her snack, and the big girl got right up in her face and threatened her.

My older daughter sees this from across the room, sprints over, and gets nose to nose with the big girl.  My 8 year old was a string bean, maybe 50 pounds, while the bully is probably 125 easy.  And my daughter says, "If you ever even look at my sister again, I'll slit your throat and watch you bleed out."  Four or five other kids heard it, and they all say that it's not what she said, but how she said it and the look in her eyes.  Everyone knew she was dead serious.  

The fat girl ran away crying her eyes out, genuinely scared for her life.  She told a teacher that my daughter was bullying her and my kid was suspended from the afterschool program.  We had several teacher conferences over the incident as well, which I had mixed feelings about since this all started because a huge 10 year old was bullying my small 6 year old.

Anyway, that's what BPD looks like in a young child.  I knew without a shadow of a doubt by the time she was 7 or 8 that something was very, very off.

PS I waivering on what level of custody to ask for, I'd opt for full legal and physical custody if you can swing it.  You may end up with something lesser, but the odds are better that all the cards would be put on the table and you'd wind up with a better situation.  My opinion based on my own experience.  I demanded 50/50 custody, got that easily.  But it's been an uphill battle since with uNPBPDexw playing all kinds of games, obstructing, interfering, alienating, etc.  Now two kids self-medicating by vaping and marijuana use.  A big hole in my case was ex's successful resistance to being psychologically evaluated.  I got mine, by the best forensic psych in the area.  She ended up with a bogus evaluation from the worst psych in the area.  This was at the end of our 4yr divorce and I was hemorrhaging cash so didn't pursue. 

If I had started out demanding full custody all of this stuff would have been correctly completed and hopefully used during custody proceedings.  Instead I became a victim of the court's incompetence.

Good for you- that's all good stuff and you're on the right path.  Just keep reminding yourself that this is not a "you-thing".  This is a "BPD-thing" and it would happen to anyone he's with in time. 

I also agree that compassion is the right mindset- in many ways, this is not his fault.  You'll probably reach phases where you hate him and that feels good for a bit, but ultimately it's unhealthy to live in that mental space.  It's okay though, you'll get through this in time and come out of it a better person.  Just know that the grieving stages are normal and they take time.

Fair questions.  Hopefully you realize though that you don't have to answer those questions today.  You have kids to worry about and your own life to live.  Focus on that.  If the marriage isn't there a year from now, so be it.  You have plenty of time though to think about what you want and what's best for the kids.

You’re right. What I was trying to say is that pwBPD sometimes mean things in the moment, but it doesn’t stick. There’s too much chaos, unstable sense of self, and impulsivity for anything to stick. So a lot of the promises and future talk are all a mirage.

Another way I could have phrased is is that very little of what they do is “real.”

This is similar to my decision to have visits as long as other people were there, as BPD mother did hold it together when others were there.

It's interesting as she embraced the identity of grandmother as part of her own image, but she doesn't have an interest in taking care of children. She's predominantly BPD and also has NPD aspects. It was mainly narcissistic supply for her but when the children were younger, they didn't notice. It was mainly my father who interacted with them. My mother seemed to observe but not interact. She also seemed to have a low tolerance and after a couple of hours wanted to leave.

When I was a teen, BPD mother related to me as if I was a confidant and also enlisted me to do things for her. She's intelligent but also low functioning. Her anxiety affects her executive function and she struggles with doing tasks and so enlists others to do things for her. She also has an emotional need for others to do this too. My visits with her consist of doing things for her. When the kids were little, there wasn't much they could do for her but as teens, I could see her start to do this with them, try to get them alone with her so she could form a one on one connection with them. I didn't fear she'd rage at them. She wanted them to like her. She was enlisting them as emotional caretakers and confidants.

I did have boundaries on her contact with them and as you would predict, and I was blamed for "keeping her from her grandchildren" which did not please my parents but I was not going to allow my mother to do that to them.