I have not read your entire sitch, but I understand you H left for OW and is now back with all the remorse? So that was me 2.5 years ago, and we are still together piecing, and there are some days that I question if I made the right choice. As time has gone by and we work on this together, I am more hopeful that we can have a great marriage. Maybe even better than before. It takes a lot of grit, patience, and time.
There is no rule book for piecing and so that has been challenging and I frequently have to step outside of my emotions and make locgical decisions. I agree with others to proceed cautiously. However when my H came back he did have all the remorse and regret; my intuition told me it was true and it was because he has demonstrated this with consistent actions over time. So I think the trust is twofold: your instincts and also his actions over time. Either way, I wish that I had let him back much slower.
Some things that helped us get through the initial shock of the separation and then coming back together were each having a good IC, going to the best MC we could find, and also reading books on how to recover after an affair. in the mean time I continued to try and focus on my own GAL/180s for me. When it came to including/telling much to the kids, we took our time on that, but my H had also moved out for many months.
Here is the thing, even if this doesn't work in the long run, or even if you don't get to a place where you feel you can accept/forgive this, you still get the opportunity to try. We are fortunate in that sense because most posters here will not have that chance. I didn't think I could or would see past any type of infidelity so that has been extremely challenging for me. I also knew that I didn't want to live my life with regrets or to not be able to tell myself (or my kids one day) that I tried. The first year was another roller coaster of emotions, confusion, and doubt. The second year was less so. Now things are falling into place. It has been a lot of work and a conscious effort to forgive and start rebuilding. There have been countless days where my heart was not in it.
Something to chew on: there are other posters here that have had their S come back to the M and even started piecing, and they still struggle because the S is not remorseful or they don't feel they can trust them. So they can do the work and start piecing, but they can't change the other--they have to wait and hope that it comes. You already have that--you feel he is remorseful and being sincere. So IMO you can now go into the hard work with a bit of an advantage.
And keep posting--here and to others-- it will help in more ways than you know.
Best of luck! Blu
“Forgiveness liberates the soul. It removes fear. That is why it is such a powerful weapon.” – Nelson Mandela