Just read this in Emma Donoghue's book "Room". Is there a word for adults who are not parents?
Doing a wikicrawl revealed these two terms:
- DINK or DINKY — dual (or double) income, no kids (yet)
- childfree — individuals who neither have children nor desire to have children
Both of these hold a lot of connotation. DINK is somewhat derogatory; childfree is almost seen as a lifestyle choice similar to vegetarianism or recycling.
As MikeVaughan proposed, Guardian seems a logical choice for someone who's with you in order to protect you in some fashion, but who is also not your parent.
May I also propose bachelor? That also implies someone who isn't married, but if that applies in your case, then this would be another possibility.
Childless adults are called Childfree.