Okay... This is quite an interesting topic that you have picked up.
Even I have read several Wikipedia synopses of many shows and several of them show this concept. Don't know why but I have always had a dislike for such concepts.
Either of the leads gets married against their wishes due to family pressure but ends up falling in love with the spouse.
Even I hate how it is portrayed... And it definitely feels odd.
Since a long time, you have been in love with a particular person but one fine day, you realise that you are no longer in love with him/her??
Okay, fine... Maan liya that you fell in love with your spouse... But aise kaise you completely forgot about your ex?? Was that not love?? Ya sirf ek attraction ya infatuation tha??
Upar se, they come up with all kinds of wierd reasons to show that the 'first love' was a huge mistake and the spouse is the perfect partner. For this, they even turn the ex into a negative character??
I agree with your views on the changes in a person and his/her life post marriage... Definitely a lot of things change post marriage and if the spouse is truly a good person, someday or the other you might even fall in love with him/her... But this doesn't mean that the ex just vanishes from your memory?? I mean you spent a significant portion of your life with him/her...so, there is some place in your heart for the other one...
Definitely... Kal Ho Naa Ho had the most realistic portrayal.
Of course you can find love twice or even more than that... aisa thode hi hai ki pyaar sirf ek baar hi hota hai.
But yes, each person has a special place in your heart and memory. It can happen that you can find love somewhere else and settle with him/her while having a good memory of your ex. The relationship does not always have to end on a bitter note...