What to do?

[Elmira]

Looking for advice. My husband of 33 years was diagnosed with Frontotemporal dementia, but his dr told me he's likely also BPD. He's been emotionally, physically, mentally abusive. I've been living apart from him, again, since March. I think it's time to divorce, but suffer extreme guilt. He flip flops between ranting via text that I should divorce and let him find a companion, to blaming me for not being willing to reconcile and give love a chance. It's been going on for 4 years and two hospitalizations. Our family is in tatters. I feel selfish to want to put my needs, my health, my happiness first. He's sick. It's not his fault. How would I feel if I got sick and my family abandoned me? This thinking is driving me nuts!

[sad but wiser]

Hi Elmira,
  It is a very difficult situation and too bad they don't say, "By the way, I have a long list of mental disorders you will have to deal with.  Is that ok?" before we agree to marry them. 
   The first rule in a bad situation is, ":)on't become another victim."  In other words, you cannot help anyone if you are not safe and strong yourself.  From what you have said, I think you must take care of your needs, regardless of his manipulations.  He is very afraid, but then, so are you!  Change always takes courage. 

[whirlpoollife]

Welcome to bpdfamily, Elmira. This site has many resources to read and learn. 
A couple of book recommendations to start out with... ."Why Does He Do That" inside the minds of angry and controling men , by Lundy Bancroft. And "Splitting" by Bill Eddy and Randi
Kreger. 
Beside articles , books , and workshops, read back to the start of some of the posts of members, including mine, to see where we were to start out with and where we are now.
After a 27 yr marriage, with young kids , the FOG was heavy. Fear, Obligation, Guilt. Xh is a blamer to this day. ( 4 1/2 yrs ago of filing for divorce and lengthy divorce). 
Marriage is not a right for one spouse to hurt another spouse with the excuse that they are mentally sick so it's allowed.
After 33 yrs for you, it is time to realize he is not going to change. 

[ForeverDad]

He flip flops between ranting via text that I should divorce and let him find a companion, to blaming me for not being willing to reconcile and give love a chance.

This is typical, the switching between two extremes.  My Ex did that more and more toward the end of our marriage.  I would leave home for work with her either raging or normal and have no way to know what sort of person I'd come home to that evening.  BPD is considered a mood dysregulation disorder.  Emotional instability is a hallmark trait.  Many of us here stuck around, longer than others would have, for some deep reasons.  We typically are inclined to be fixers, co-dependent, etc.  The ever-changing moods were so confusing and left us confused and stuck as "deer in the headlights".

Whatever his reasons - and you cannot discount manipulation and gaslighting to make you doubt yourself - you have to deal with What Is.  Wishes and hopes are not practical ways to plan or secure your future.

Have you watched the 1944 movie, Gaslight?  An innocent bride is manipulated and confused by her (nefarious/criminal) husband as he convinces her to doubt her own sanity.  That's where the term 'gaslighting' comes from.