Is terylene a copolymer?
No, PET it is definitely not a copolymer. Neither is e.g. Nylon 6,11 (or any other polyamide with two numbers). The monomers alone would not polymerise, or at least only by a very different reaction (e.g. ethylene gylcol gives PEG).

What you can have are alternating copolymers, but there the sequence is a statistical property. It comes when a reactive chain end B* has a higher probability to add an A (to give BA*), and a chain end A* to add B (to give AB*). That probability is sensitive to monomer composition, the temperature, pressure, catalyst, etc. If you want to read more about that, "copolymerisation parameters" is the topic to look up. The monomers you see there are afaik invariably olefines, i.e. they have a double bond that undergoes polymerisation.