What's up with these fish?

I just started a small tank which holds 2 goldfish, 1 gold, the larger of
the two and 1 smaller black one
he/she looks like a black molly. The larger of the fish spends pretty much
of his/her day chasing and nudging the black one. As of late, there has been
alot of rubbing up against each other as well..The gold one is almost in a
frenzy when the black one hides out from him (or her)

Then they'll get earily quite and hang out together in a corner of the tank.


I should mention that the black one does not have any bite marks or pieces
missing from his fin.

Could they be mating? How long is the gestation period? What do the babies
look like?

thanks
debby