So I hear some people don't like Big Macintosh/Cadence, which is fine — I'll just draw Cadence/Blueblood instead! Enjoy! x)
Anyway, the relationship between Prince Blueblood and Princess Cadence is not exactly a secret, it's just lowkey because a.) they're not exactly 'dating' anyway no need to get everypony to thrust their nose into their private affairs and b.) if it ever became obvious, they'd have to stop due to the scandal — so when they're forced to behave like proper royalty they just share a casual smile and a glance into each others eyes when they pass each other — promising that they'll find time together later. Celestia kind of just exists in a perpetual state of denial when it comes to their relationship. There's really a lot Celestia is in denial about when it comes to these two.
(When Big Macintosh is in town she's exclusive to him, when he isn't she's — with his blessing, since he knows just how badly Cadence needs companionship and distraction to withhold her depression — free to see others and that's mainly when she and Blueblood have the romantic/sexual part of their relationship.)