If I succeed in the practice of contemplation of physical
uncleanliness of the human body, it will lead to the following
outcomes for me:
1) Not only do I eradicate lust from within, I will also become
a guy who has no desire for any woman in any way, except for
friendship or considering them as if they are my biological
sisters.
2) Following number one, this will mean:
a) If I'm not married, I will not have any desire to be with a
woman in any romantic sense. This means I will not have a
girlfriend. Even if I do, I will probably initiate a peaceful
breakup with her.
b) If I'm married, I will probably go for divorce. I have no
desire for this woman who lives with me and sleeps next to
me. I have no desire to regard her as a woman in the romantic
sense. I will just go back to treating her as a close friend. Of
course, if I already have kids or my wife is pregnant with my kid,
this won't be easy. I won't go for a divorce immediately. I will
wait till my kids are financially independent or quite grown up to
at least earn a living on their own, before initiating divorce. In
the meantime I will sleep either with my son or sleep in the living
room.
There is a trend in which young married couples put off having
kids altogether and some even go on without marital sex at all
throughout their marriage. Imagine if these people had practised
Buddhism and succeeded in the practice of contemplation of physical
uncleanliness plus understanding how love between man and woman is
a form of craving and that it leads to endless samsaric cycles of
birth and death, I don't think all of them will stay together as
couples any more. They will totally devote themselves to inner
cultivation.
The above are my personal views of what I would likely do if I
succeed in the practice of contemplation of physical uncleanliness.
So it does not apply to everyone. But I would like to hear what
fellow Buddhists have to say about application of this practice and
what would they do when they are in a romantic or marriage
relationship with the opposite sex.
My personal view is : if any person who suceeds in this
contemplation practice before they even start to have a romantic
liking for a member of the opposite sex, I can almost be very sure
they won't have any girlfriends or wives throughout their lives
anymore. Cos all are their friends and sisters, nothing more than
that.
If you succeed... you can still love sentient beings but not
their bodies. You don't just see appearance but their Buddha
Nature. If you do, you're a Bodhisattva 
That said I have seen enlightened people who still continue
their relationships without breaking up. You can still be close
companions, even spiritual friends. My dharma teacher and his
husband are very close, but I do not think they maintain sexual
relationships.