The power doesn't have any rules that says it lasts for longer than a combat round, either. So, by the rules on duration on page 114 of the WT2 rulebook, Bind lasts one combat round. After that round, you need to roll again to keep binding the target. So, yes, you'd have to add Duration or keep rolling each round to hold the target in place for a full combat scene, or keep rolling each combat round.
The target can break free that round by making an opposed roll.
If you want to attack multiple targets in a round, you have to do it as a multiple action, or modify Bind by buying an extra like radius.