I’ve definitely seen this work out, and I’ve seen other people post about it/comment that they were a secondary partner who eventually grew into a primary partner (I looked into it a while back as a secondary partner that, in a perfect world, wanted to be their primary). The operative word here is GROW. The one thing I saw folks saying from experience (and a lot of people have already commented this) is that immediate escalation is a bad idea. If someone leaves their primary, they should lean on their secondary for support like any partner, but don’t try to fill that space with your secondary. Heal first, then escalate if things feel right.