Hm, I don't know - we need to remember that this is all "a year later". Lancelot have disapeared for what - a year and a half now? - without a word, and Arthur has been on uncertain standby for about as long, with the very strong possibility of 'never, ever'. The life-span of someone in Camelot must be very short to start with, what with all these wars they have going on, so each year must be like a clock ticking. Considering all this, I don't see it as 'wavering' of her to look out for new prospects (one-nights or otherwise) when the others have all fallen out for all this time - and it might even finish the messy breaks properly with everyone happy. And even then, it's a huge extrapolation to think that because she smiles back at a known flirt, she's wanting to have somethnig steady with him, instead of simply enjoying a friend and a flower.

Though I must say that there's a lot of expressions used when describing Gwen's various love interests (even when they are one-sided) that put me on edge. Namely, that it's completely impossible to love two persons at once, to want or to consider safer someone or something that isn't the love of one's life, or that showing interest of any type of liking counts as flirting, that it is wrong to be able to seek love, companionship, and lust in different people in any combination, or that liking several people at once is a flaw and makes someone inconsistent and their love for any of these people less true.

People's definition of what romantic love is and isn't varies between everyone, but in mine these situations all make sense, and none make Gwen look like she cares less about Lancelot or Arthur. But some contexts could show she would like to. (I'm biaised though, because my current relationship falls under one of these umbrella. There's ways for any of these things to end up being what people are calling it right now, but it's not my default because I can see how it could work with everyone being happy, I guess.)