I've read a TON of infidelity-related books (I should have invested in the publishing houses on dday I've spent so much $$ on these damned books). I've yet to find anything that specifically relates to LTAs.
But if I had one piece of advice for any BS - including those suffering from an LTA - it would be this.
Read the 2 books you mention. Review/re-read as needed/desired.
Then - ditch the infidelity related books. They either say the same things you've read in the 2 you mention, or they are going to piss you off bc they are subliminally - or sometimes outright- blaming the BS (and this includes the WS-sympathizing bullshit spewed by Esther Perel), or they will be long on theory but short on practice. There are a couple of exceptions, and I may re-read some now that I'm in a less fragile state, but NJF and HTHYSAYA are really ground zero, IMO.
First read at least one Brene Brown book (I've read all, but recommend Rising Strong - I'm probably partial bc it was the first one I read).
Read Rick Hansen's Resilience - and do ALL of the exercises (I suggest getting an audible version [I borrowed the CDs from my local library and ripped them to my iphone], so you can actually do the exercises by listening vs reading what to do - just makes it a heckuva lot easier).
Meditate - every morning and every night if you can (I use an app called Insight Timer, but there are tons of other free ones for a smartphone).
Then read (or watch videos) of Pema Chodron.
IMO, healing from an LTA is the same as any other A. You have to heal you. No one else can do it for you. It sucks the bigtime, but it is what it is - the sh*t sandwich must be digested to move on.
The biggest difference is that one must process years of betrayal. For instance, with an LTA, there is no "affair season". For some it may be a blessing - for others, a curse (in that EVERY day is an "affair day" with an LTA). But what's worked best for me is working to find joy in whatever I can - the more time I spend being happy about seeing a snake in my yard (I think nature is pretty cool), the less time I'm miserable thinking about how many bites of that f*cking sh*t sandwich I've yet to eat.
Working (and this is REALLY REALLY HARD) to stay out of total blame and anger. Blaming and shaming my WH may make me feel good for a bit - but ultimately do nothing for ME other than fan flames that keep hurt alive. Yes there are times where it's all you can see - and we all know that venting is Ok (I try to do it in my journal or here on SI, but I'm far from perfect and my WH can attest to times I've been far less than my best self), but overall, does it really help heal? They are far easier than working on figuring out who I want to be, and how I want to live MY life in the wake of the sh*t sandwich I've been served.
Again - these are things any BS must address.... how will I move forward to be the best person I can be? How do I work on MY life - and what it looks like WITHOUT my WH? If it turns out that my WH is "R material" and I am ultimately able to find forgiveness and peace with him - great! But the really hard and scary part is fully facing the opposite - my needs and wants completely separate and apart from WH (there is SO much truth to letting go of the outcome. Took me MONTHS to come to terms with it, but for me, it's been a big milestone). I still struggle every day. It's hard to allow the painful feelings to come through and be processed without getting stuck in my own little pity party.
Of course, none of this may resonate with your friend. We are all different - even those of us in the LTA "camp" of this sh*t sandwich.
[This message edited by gmc94 at 4:23 PM, December 10th, 2018 (Monday)]