So the front end of any opamp (except extremely high speed ones) or comparator is a differential
pair (aka long tailed pair). That's the circuit to play with first. and understand. A common
design for any low frequency differential amplifier is differential pair as input, driving a current-mirror
load. That should be enough search terms to be getting on with!
Both comparators and opamps are forms of high gain dc-coupled differential amplifier, using a
differential pair input stage.
However comparators are designed to be fast but not stable, and drive a logic signal (usually
Opamps are designed to be stable with large amounts of negative feedback(*), often low noise,
and to drive a modest analog load in a bipolar fashion.
(*) in practice this means the gain is deliberately made to fall with increasing frequency.