Gaeta always keeps appointments. He is, therefore, at the convenience store to meet Martha even though that's one of the last places he wants to be right now. It's not that he doesn't want to see her—he does—but he's almost certain that things are going to go horribly. They'd gotten perilously close to arguing the day before, and Martha hadn't seem convinced that he'd truly forgiven her. She might take any flinching or shying away on his part as proof of that.
But he's as prepared to talk to her as he's ever going to be. Presentation is a large part of success and Gaeta thinks that he's sufficiently composed and put together to hide his uneasiness. It's an act that has served him well in the CIC and on New Caprica; surely it won't fail him now.