Why Super Heroes have failed-in love / married life?

 Flat Character Arc - Love and Marriage: Flat characters are also sometimes referred to as “one-dimensional” or “two-dimensional." A flat character will typically:

• Have no internal conflict
• Conform to a stereotype
• Never experience character development
• Lack a multi-faceted personality

Flat Arc Characters usually get attracted by Positive Character Arc Characters. The love life of Flat Characters isn't as successful as other Arcs. When they get married to another Flat Arc Character, they may have a long marriage life but mayn't have a satisfying life. This is because, both the Flat Characters have already gone through a phase that has given them a lesson. Love or Marriage is just a part of their life.

Flat Arc Character's love stories aren't as glamorous as those of Positive Arc Characters. They miserably fail to attract Positive Arc or Negative Arc Characters to make them their love or a life partner.

Peter Parker falls in love with Mary Jane when he is in a positive arc. The same person after undergoing a several event becomes Spider-Man (Flat Arc). Hence, Peter Parker struggles to live between his Love Life and Public Life. The same applies to all the Flat Arcs. Same happens with Batman, Ant-Man, Super Man etc. In real life also, the love/marriage breakup happens for humans with a flat arc VS other arcs.