You know what I'm tender about? This moment of character development for Margaret ultimately hinged on the fact that, A, Hawkeye was gone, and B, BJ was there.
Even though by this point, Margaret and Hawkeye are beginning to become friends, I don't think she would have allowed herself to be so vulnerable as to extend an invitation to spend time together if he had been in camp. Not only do they still have a mountain of past baggage to work through, but she knows Hawk too well. He would've made some kind of teasing, innuendo-laden quip and she would have balked and retreated. However, BJ is a safer bet. He and Margaret don't have that long year of torment and harassment hanging over their heads the way she did with Hawk and Trapper. Even still, if Hawkeye had been there, then BJ would have immediately let him take the lead of the conversation, and again, Margaret would have fled. And if Charles had been alone here, then I believe Margaret would have second guessed her invitation. She's still a married person, after all, and he is not, so in her mind they really should not be spending time together with no one else.
But BJ is different. He's the one who gives her a grin and a wave in parting whereas Charles doesn't give Margaret a second glance. When she calls out to them, he's the one who keeps his tone light and his smile easy. He's the one who speaks for him and Charles rather than letting any kind of awkward silence linger that might cause Margaret to withdraw. He stays so open and amiable and, though visibly confused, is still open to whatever this strange change in Margaret is. With very little effort at all, he makes Margaret feel so at ease. If he hadn't been there and if Hawkeye hadn't been called away, who knows how long it would have taken for Margaret to be brave enough to open herself up for the possibility of rejection? And if she hadn't had this fledgling moment of friendship met with such warmth, who knows how long Margaret might've been satisfied living off the crumbs of affection from a husband who never cherished her like she deserved?
