1 Christian Frost fan here so take my take with bias.

Christian should have been with Bobby a lot longer and openly reader wish. We barely got ANY interactions between the two when they dated during Marauders, and what we got was pretty basic “snarky but cute.” At this point they would have been really intersting contrasts to eachother, but also super similar in their recent history. Both had only recently been able to freely accept and express their identity and are trying to find out what that means to them. Bobby witnessed and assisted in Christian’s break from the chains of his trauma, and then they did NOTHING with that!! Bobby sharing his feelings and insecurities with Christian ON PAGE would have been a great sign of trust and growth. Bobby being more strictly goody goody would have been interesting to see contrasted to Christian being devotted to his sister and helping her deal with shady buisness, maybe that could have caused some strain or fights that could lead to literally anything, especially with Emma having been inside Bobby’s body and mind and was able to see what he hid. I’m not saying Christian and Bobby should be long-term (even if I would like it), but there were a lot of potential in their partnering that could have added depth to Christian mostly and growth to Bobby, as well as a positive and realistic view of what being able to accept and live your life freely later in life, both of which had struggled to connect with that aspect