But the classic conundrum here is that no one wants to be in charge.
Two firstborns often butt heads, says Cane, because both want to be in control of every situation.
Take that into consideration and make compromises to keep the relationship solid.
Oldest with Middle This can be a fine pairing most of the time, but the middle child's tendency to mold herself around her partner may leave her in danger of not following her own dreams.
Relationship Tip: Try to figure out which of you is best at certain tasks (such as handling money or making decisions about the children), and then own up to that responsibility, rather than assuming the other will take care of it.
Onlies with Anyone Unlike the other birth-order positions, only children haven't been studied as much, says Dr. "Most people assume an only child will resemble a firstborn in relationships," since they are, after all, first, but that doesn't take into account the fact that an only never had an advisory (or bossy! An only with a firstborn can be a good match if the only child acts less classically "firstborn." And an only with the lastborn can present issues, says Dr.