Being on top

I've just started my sexual life with my boyfriend, even the first time was great (obviously hurt a lot but it was good 👌🏼), we change a lot on positions and the rhythm helps a lot, bus he puts on top and I honestly don't know what to do, when I'm moving he always got out and sometimes I hurt him because it bends...
Any tips? He likes me on top and I want to be better...