They're close. I know that much -- he cares for her. [Loves her.] It's always been my impression that she, too, cares for him.
[But he obviously won't just stand by and let her use him -- because, well, the similarities of the scenario being presented don't escape him. It sounds like Athos. And he knows how much Athos suffered because of Milady.]
[His expression softens, very briefly, at the next part, though. Because, well, he's already told Aramis as much that he's one of the best parts of his life, too. Although perhaps he should be worried it's so obvious to others.]
[He doesn't get a chance to say anything more before Sherlock starts to walk away]
[Walks after him, grasping his arm] Wait. What, if anything, are you going to do about any of this, then, other than telling me?