Say what you want about the sometimes-villain, sometimes-X-Men-member Mystique, but you cannot deny that the girl gets down. There have been many Mystique lovers over her nearly 40-year stint in publication. Mystique hook-ups are pretty common, but she's had her share of long-term relationships, too.
Given her near-immortality due to her mutant shapeshifting ability, there are bound to be a great number of Mystique boyfriends and girlfriends. The lady knows how to get her some, so we have to give her credit for that. Take a look at this list of lovers that Mystique has taken to bed over the years.
Wolverine's healing factor and Mystique's shapeshifting ability make both mutants near-immortal, so the two were bound to bump uglies sooner or later. Before the X-Men were even a thing, the two bonded over the fact that they were different from other folks and toyed with the idea of running off together. Too bad that it didn't work out and it lead to a bloody feud between the two that would last for nearly a century.
So while lying low for a while, Mystique took a more human appearance and married a rich baron named Christian Wagner. Sadly, Wagner left Mystique unsatisfied. So she was seduced by the devil... literally. Azazel is an immortal, demon-like mutant that is so old he actually is Satan and Beelzebub from the Bible. Their carnal union would result in another pregnancy for Mystique, giving birth to the mutant hero, Nightcrawler.
In Deadpool #27, the Merc with a Mouth talks to a bartender and outs him as Mystique. The two mutants then pull guns on each other. So what is this all about? Revenge? A gunfight to the death?
Deadpool just needed Mystique to sign some divorce papers. Because they were married. Yep. Deadpool and Mystique were married. Now, just got divorced. Not annulled. Divorced. Which means the marriage was official and consummated. With sex.
You can try to stop thinking of the horrific image of a grinding pile of Wade Wilson's pockmarked flesh merging with a blue shapeshifter, but I don't think you can.
Mystique's relationship with Irene Adler, also known as Destiny, is Mystique's longest and arguably most loving relationship. As far back as 1981, X-Men writer Chris Claremont intended both characters to be lovers and even suggested that Mystique would shapeshift into a man in order to impregnate Destiny. The big reveal would be that the two women were Nightcrawler's biological parents.
However, a combination of the Comics Code Authority and Marvel's own policy at the time forbade the outright depiction of homosexual and bisexual relationships. Not to mention the cultural hang-ups regarding transgender people. So instead of two women being Nightcrawler's parents, it was Mystique and Azazel. Remember kids, back in the 1980s, it was okay for a demon to be your dad, but you couldn't have two mommies.
As time moved on, the X-Men books would acknowledge the then-hinted relationship Mystique and Destiny shared.