Being single is never a problem to me? or being single was never a problem to me?
It depends. If it's still not a problem to you (and most likely never will be), then "is." If it used to not be a problem but is a problem now, then "was."
- He is never sick. = He is always healthy.
- He was never sick. = He used to always be healthy, but now he gets sick.
- He is never sick. = He is always healthy.
- He was never sick. = He used to always be healthy, but now he gets sick.