Love marriages are mostly due to attraction. When attraction ends it also ends.
Second thing it is lacking the approval of their parents from their heart so parents also not bother on breaking of such relationships.
Both of them were having lots of expectations with each other which are not fulfilled now. So this will lead to quarrel between them which fills their life with hell like experiences.
Whatever promises they have made to each other earlier are not able to fulfill leaving each other unsatisfied .
So it ends up with bitter unforgetable experiences.