Not necessarily.
in HxH Gon and Killua never fight each other and the thing that i love so much about it is that neither one acts all butthurt when they're getting outshined by one another. They don't get jealous of each other and never fight each other.
HxH
YYH
JJBA
FMA
Toriko
Just a few series where the main protagonists don't fight each other.