When I was watching "Something Borrowed", the sharp contrast between the trio of Jack/Gwen/Rhys and the Doctor/Rose/Mickey was brought to mind.
They're a similar set-up with an opposite choice by the leading lady. Both Rose and Gwen have a steady man, someone that they can rely on, and then they meet a man who turns their world upside down and introduces them to a life that they take to like a duck to water. In both cases, the steady guy learns about the new lifestyle and is willing to support/join in. Gwen chooses to marry her reliable guy, the one she can always count on to be there in the morning. Rose picks the riskier choice, the guy with the mysterious past and unpredictable future.
And (this is the fantastic part to me) neither of them is shown to be making the wrong choice. Both options are considered to be valid. Each woman makes up her own mind.
A similar contrast can be seen in Tosh/Owen versus Martha/Doctor -- in one case, unrequited love paid off and in the other, it didn't. No character is vilified by the shows for having feelings that aren't (currently) being returned, yet the shows acknowledge that sometimes loving someone who doesn't love you back the same way ends up with requited love while sometimes they really do just want to be friends.
It's incredibly mature storytelling that respects both individuals and their choices. Another case of this is in Ianto/Jack/Gwen, where Ianto and Jack are sleeping together, Gwen and Jack have UST, everyone is aware of both of these things, but Gwen and Ianto are great mates.
*squishes their adorable cuteness*