Divorcing Dstbx- why am I hesitant to file after 1.5 years apart?

[Wits End Woman]

Hello all,

I have not made my introduction yet; I'm currently working on the synopsis of our relationship but in the meantime I could really use some of your thoughts and opinions on why I might be having second thoughts about finally filing for divorce. 
We have been married for 10 years, together 12.  He's cheated at least 3 times that I'm aware of, lied and broke part of my extended family apart with his behavior, we've had many blow up arguments where I was afraid of his next move.  Separated a couple of times in those 10 years but always came back to each other.  He was diagnosed with BPD, ASPD and negativistic traits, severe PTSD, anxiety and depressive disorder about 10 years ago before we married.  The only diagnosis I was told was PTSD and depression. 
I have been dating someone else for about a year and he's a wonderful person.  Actually normal!  But every time I find out about a girlfriend of ex's, I lose it.  I don't know why!  I recently found out about a new girlfriend and I have honestly thought about giving it one more shot.  What's wrong with me?  We always said we were soulmates and I truly feel that way.  But how can it be so difficult to be soul mates? Why does it feel wrong for him to be with someone else? I appreciate your thoughts. 

[ForeverDad]

Historically, infidelity has been an undisputed reason to divorce.  In the New Testament Jesus referred to adultery as a valid basis to divorce.  So if there have been 3 affairs, that you were aware of, then there is no doubt you are justified to divorce.  Yes, you separated, but it seems it was only a timid half-step forward.  You can choose your path.  Leave the past behind and move forward.  Understand that the first step is very hard.  But each subsequent step gets progressively easier.  Been there, done that.

However, emotionally you're still holding onto what was.  So while it is understandable that your head got the message before your heart, what's bogged down the Let Go & Move On process?  Why are you still looking back rather than looking forward?  Have you looked at the articles on Grieving a Relationship Loss?  The last stage is Acceptance.

Can you accept that going back would be getting back on that endless roller coaster going nowhere good?

Can you accept that you need to move forward with your life?  Seems like you have a foot behind you (still married) and a foot before you (a new relationship).

One thought often mentioned here is to close out the old relationship, then giving yourself time to recover so you don't jump into a rebound relationship.  I'm a bit concerned that your separation kept you feeling still connected to him and the new relationship was affected by that.  What do you think?