In terms of the actual game, we simply have such a vast number of people playing their miqo'te that the initial description of the female/male ratio sort of already fly out the window. It's normally, I believe, supposed to be something like one male born for every ten females. I've honestly seen that one lampshaded by some in the roleplaying community on Balmung, and I've also seen one RP FC actually put a recruiting ban on Miqo'te because they're so populous.
From what I can discern, many Seeker men of a strictly tribal mindset would consider the concept of monogamous marriage to be limiting or, even beyond that, a threat to their genetic legacy. In slight contrast, I've seen Seeker women roleplayed under the opinion that marriage would be selfish from a tribal point of view because it forcibly ties two people together, which can limit a person's independence.
I've seen more Keepers amicable to the idea, both male and female, largely because the men aren't raised to compete so rigorously. In a lot of ways, they just do what they're told, and if a female decides to keep one and nobody minds, then who would care?
Again, this is all from a strictly tribal point of view. The land of Eorzea is, and has been, changing greatly in recent years. New ideas are spreading like wildfire, and one's race is slowly beginning to have less and less impact on one's place in the world than one's other merits. Not only that, but there is nothing stating that one's character is required to be chained down by her or his tribal roots. A difference of opinion might well be one of the reasons your character left home to begin with, or your character could even have just been born in a city and exposed to different types of lifestyles from childhood on.
And there isn't any clear cut rule stating that a nunh is required to father children with 50 different women, or for a Keeper to never have a child with the same male. I would honestly be completely shocked if monogamous love didn't just sort of happen now and again.
I roleplay a Seeker male, and he is of the opinion that marriage is 1) weird and 2) something he can intellectually respect and understand. He is a tia, a non-breeder, and he doesn't ever plan on being a father. He has fallen in love with a single person, and having done so was actually an interesting plot point in its own right because he openly admitted that it wasn't how he was raised and it bothered the heck out of him.
Had the relationship not gone down in flames and tears, who knows if it would have gone there or not. Part of the actual fun of the romance from a roleplay perspective WAS that he and his partner had to have a lot of talks about how they fit together and whether or not they were comfortable with it, as well as sort of what love means in general and why it exists at all.
Had they not ended the relationship, maybe it could've eventually gotten to the point of marriage. I and the other player hadn't ever mapped that out.
...To end this post, since it got way long, I'll basically summarize by saying that it would seem to me that a Keeper would have an easier time with it than a Seeker, but that every person is different, and that includes their personal beliefs as well. There are no hard or fast limits in lore that would corner you into saying "My character would behave or believe thusly". Only tendencies.