To everyone who hoped for Sun to wear a dress as maid of honour, during the big wedding. I see ya!
But I also see why that didn't happen and he instead wore a suit.
First of all, Sun in a dress would outshine Terra too much, and that's simply not fair to the bride.
Secondly, it would have been too big a sudden jump back into femininity.
Sun had it bullied out of him, hard, by Old Moon back in the day. Even dressing up as a princess for the kids in the daycare was mocked, and we all know how rough Moon was about the mockery back then. Then came the jokes at Sun's expense of being gay, bi, a femboy, anything to bully him for being soft and unmanly every way possible.
And yes, quite the irony of mocking Sun for not being manly enough, from people that are genderqueer and genderfluid. But Sun simply is an easy target, because he takes it all in and carries it with him.
What is needed is him gradually finding his confidence back in his masculinity. It won't happen overnight, it will take time and small steps.
Letting Dazzle practice makeup on him, is a great start. Although he was clearly uncomfortable with everyone seeing and commenting on it. I'm sure as Dazzle explores more subtle makeovers, in less crowded settings, it'll go easier.
And his mentor, Dalhia, being a male openly presenting female just for comfort, will be a good role model to help Sun along, the more they get to know each other and relax.
Just my 2 cents