Depends of how is use, sometimes being too invested on something or somebody, make you forget to attend other necesary aspects of your life and doing some rash decision thwt might not be good for your long term interest. Maybe is a flaw and a virtueI'm walking into semantics territory, but I'm not sure having feelings or caring too much are really flaws. It makes his job harder, but that's not a flaw. It's not like alcoholism, or being attracted to underage kids.
As for Superman's flaws, i always thought that it was the fact that is very difficult for him to swicht off his hero mode, tragedy is always happening or about to happen and he can't be around all the time, but he tries and left other aspects of his life unattended, mainly his relationship with people that don't know his secret identity.