In an earlier scene Olenna made it clear to Margaery that if she is to have any influence on Tommen over Cersei going forward, she would have to press the advantage now. Heeding her grandmothers advice, she sneaks into Tommens room at night, which must have been quite the pleasant surprise for the boy. There she lets him know that they are to be wed, so they might as well get to know each other. They make a pact to visit each other in secret. Once again we get to witness Margaery do what she does best, and ignite interest in her future husband by appealing to his personality. Whereas with Joffrey she appealed to his sadistic tendencies, here she does so to Tommen with kindness and innocence. The difference is that you dont get the sense she's lying or manipulating for its own sake, something that hasn't always been the case with her. She's always come off as a genuinely kind person, which makes Tommen a much better match for her than Joffrey, whom she had to feign interest in. How successful she will be especially with Cerseis constant presence remains to be seen, but Tommen sure looks happy to be along for the ride.
