as far back as 1981, chris claremont had intended to reveal nightcrawler to be the son of mystique and destiny; with mystique taking on a male form for the conception. this was hinted at many times in the early 80’s, most notably in uncanny x-men #177 (1983) when mystique refuses to kill a robotic replica of nightcrawler during her training.
however, this concept was never allowed to come to fruition and azazel the demon lord was written to be nightcrawler’s father. indeed, it took marvel over ten years to openly state that mystique and destiny were in fact lovers.
because of marvel (and the CCA)’s “no LGBT characters” rule being in force at the time, writer chris claremont was forced to skirt around their relationship, using terms like “beloved friend” to imply a deeper connection. other examples of this include the domestic life they lead whilst raising rogue and how the shadow king refers to destiny as mystique’s “leman” (an archaic word for lover) in uncanny #265 (1990). the extent of mystique’s mourning when destiny dies also implies that the nature of their relationship was more than friendship.
the policy that prohibited the “outing” of this relationship was enforced by then-editor-in-chief jim shooter. it would be all too simple to chalk shooter’s reluctance to allow the relationship to be acknowledged down to homophobia, but i think there’s a lot more to it than that.
i think the main reason that shooter wanted to steer clear of LGBT characters in comics is his previous experience with portraying similar issues. in addition to being editor-in-chief, shooter also wrote for the company. back in those days marvel would regularly side-step CCA regulations by publishing stories in magazines, which were not subject to CCA rule. shooter’s story, “a very personal hell”, from the hulk! #23 (1980) chronicled bruce banner, on the run for some hulk-related crimes, stopping over at a YMCA. during his stay he is accosted and almost raped by two men: