I think there are two levels to this: One is the superhuman v. normal person side, which a few comments here have hit on. Absolutely these are what I would call “comic” reasons they don’t work out. The second has nothing to do with powers or not. This is the way they relate emotionally about the superhero stuff.

The last panel with them deciding to break up is beautiful from an emotional maturity level for both of them. Mark shows up to tell Amber he can’t be what she needs, and he feels it just isn’t fair for him to even ask her to accept what a life with him demands. Instead of some terrible response, she agrees. Set against both of them at least emotionally cheating on the other prior to this conversation this exchange is… refreshing.

You have two relatively adult people seeing a rift that cannot be solved between them. And instead of trying to make this into a fight (after some rough spots), they are able to recognize the problem and realize it has no solution. In the comic the root issue IS superhero related, but you could switch this to some other root cause and the beauty of the resolution remains. Desire to have kids, differing views of relationship roles, career ambitions, etc… You could have a root problem in many ways, and the scene shows both Amber and Mark have the awareness of themselves and the other person to see there is no resolution.

Yeah, maybe I read too much into it, but the underlying message is actually great. I wish more people had the ability to see when a relationship is just doomed despite love, and agree to move on in way that leaves both people able to appreciate and care for the other, but still move on to something healthier.