Would you then not find it hard not to give said individual special privileges?
In Mass Effect 1, I found I was treating Ashley quite differently than the rest of the characters. She would always be with me when I went out on missions & I made more attempts to talk to her.
Do people take those marriages seriously?
I mean do people start taking these marriages as part of their real lives and start to dismiss other parts of their real lives?
I wouldn't say that I began to dismiss the other parts of my life (but I did spend a large portion of each evening playing the game).
...but for normal humans?
Another game [series] you may want to check out (for reference purposes) is FABLE 2. You could woo almost any character. It even had some interesting statistics (# of STD's contracted, # of people slept with, etc.). There were even funny 'cut scenes' where the woman (I was a man) would say, "OH! Is that it?!" or , "That's how I like it - short and sweet".
Personally, I am a fan of relationships in games. I like to know [and to get know] the people I travel with. Just like in my real life. I like to know the people I work with. I talk with them, laugh with them, empathize with them, etc. But that could just be me.