BW here. I spent a LOT of time on the suicide hotline and websites for months after dday. I still have moments where I struggle. FWIW, I do not consider my WH and I to be "in R", as he has not shown himself to be "R material".
Everyone is different, but there are things that I would have loved to have seen from my WH.
First would be that he take a PROACTIVE role in healing and recovery. That can mean a bunch of things, but for me it would have been communicating his thoughts, getting over his conflict avoidance, talking about the A, and no more lies (as we begin year three of this shitshow, he is still conflict avoidant [tho there is slight progress in the last few months], still doesn't communicate [again SLIGHT progress only recently] and last time I caught him in a lie was, I think, over a year ago, BUT I can't say he's stopped as I stopped snooping to check [I guess I just decided that it wasn't worth my energy to continue to expect honesty or check up on him, so I kind of assume that he's lying most of the time, which is NOT a good thing])
Triggers are a bitch. Learning what may trigger him and asking what you can do in those moments can help. Maybe not, but it's worth the discussion (and bonus! If you bring it up during a calm moment, you are bringing up the A).
Learning about apologies - esp those from How to Help Your Spouse Heal from Your Affair. SPECIFIC apologies for SPECIFIC actions and the SPECIFIC consequences. Just saying "I'm sorry you hurt" is not enough. The words you use MATTER.
Learn about trauma - for both of you. If your BS is suicidal, I'd say learning about trauma generally, and relational betrayal trauma specifically is pretty important.
I HIGHLY recommend the body keeps the score by Bassel Van Der Kolk. It's a long book. It has nothing to do with infidelity. It will help you understand what trauma is, how our lizard brains go on high alert, etc.
For infidelity specific trauma, I'd listen to the Marnie Breecker and Duane Osterlind podcasts. There is a 2-part interview with Breecker on the Addicted Mind (you can google it). Then the two of them started Helping Couples Heal last year. They have several episodes (about 30 min each) that I have found helpful. At a minimum, just listening to the Addicted Mind stuff (2 episodes, I think about 45 min each) will help you realize just how deep this trauma and hurt are.
FIND EMPATHY. Read about it. Brene Brown has some great stuff on this front. I recently listened to an older audio recording of a series of 6 (I think) lectures, it's called The Power of Vulnerability (from Sounds True). I got it via my library on Hoopla. I've found it to be the best audio from her that I've come across, as she really lays it all out (shame, vulnerability, numbing, authenticity, etc and then the last episode or two are recaps. She has great data and an easy to listen to style).
I loved Resilience by Rick Hanson (on audiobook, which I also got for free from the library). His HEAL steps have been life changing for me (and I do attribute it as a major factor for me still living on this planet). Those steps can help BOTH of you learn resilience when dealing with the rollercoaster.
I gotta run, but will try and come back later to add to this.