Look, I personally don’t think Balth got back together with Damien out of some weird passive aggressive revenge reason- I think it was fear of actually dating the guy he’s built up in his head so much over the years. It can be really scary to have something like that actually become possible and having to question whether you love a person or the idea of a person.
It also totally isn’t Peter’s fault they’re not together, as after Balth’s probable ignoring of the issue and getting back together with his ex… That would seem like a clear message, especially as Peter was in such a self loathing headspace. He might have thought Balth didn’t think he was worth it after the events of NMTD.
IN CONCLUSION: I am confused and refuse to place blame on either of these guys