It's a known fact that powerful people - especially in autocratic regimes - enjoy considerable access to sexual favors (witness Beria, or members of Saddam's government for well known excesses).
I think that is reasonable to assume that the Emperor's right (post-ROTS Darth Vader) hand took advantage of the (probably a lot of) ways of "entertainment" at his disposal.
But I want to know if this indeed happened as a canon (Legends or Disney).
To clarify, (as @DampeSBN pointed out in comments), sex is not limited to genital contact - I'm interested in any activity/relationship that may be deemed sexual.
P.S. As far as Vader's plausible motivation, I was specifically thinking about a hypothetical situation in which Darth Vader became interested in a "escort" (or your favorite slang word) with a physical resemblance to Padme.