Ben Affleck is Ultimate Instagram BF for Ana De Armas in Costa Rica

Ben Affleck's already got a handle on the Instagram boyfriend lifestyle -- he's happily snapping beach shots of his hot new girlfriend, Ana de Armas!!!

The couple's down in Costa Rica for a romantic getaway after finishing filming on their upcoming movie. There have been plenty of rumors about them hooking up, but these shots of their romantic stroll confirm it ... they're totally smitten.

Ben couldn't take his eyes off his "Deep Water" costar during Tuesday's walk in the sand -- and not only because he was taking pics of her. When he wasn't behind the lens, Ben got up close and cozy ... snuggling with Ana on the beach.

The PDA proves the chemistry just keeps flowing between these 2 after playing husband and wife for the big screen. We recently saw them in Ana's native Cuba, so things are definitely heating up.