A story that has repeated itself many times in history: A boy and girl fall in love. They want to marry. Then people tell one side that the other side is trouble and not to go further. The person is in love so he/she ignores all warnings. Then they marry and a price is paid that is beyond anything the person ever imagined. Financially, emotionally even physically [as it takes a serious toll on one's health].
I have been involved in a number of such cases. Sometimes, people [mistakenly with good intentions] defame the rabbi/s who are against and encourage the conflicted person to go ahead with it. Ahhhhh - but those who try to push it through are not the one's who pay the price.
So sweet friends remember - love is all too often fleeting. Make sure your relationship is a lasting one. Listen to the council of elders. Do your research. As my cousin pointed out in his sefer הליכות עולם, it is only lashon hara if it is רע - evil speech. Saving one from a disaster is not evil. It is a massive mitzva. To see people broken by marriage is heartbreaking. Try to avoid it yourself and to help others avoid it.
That being said - not every silly piece of slander is necessarily true or significant. So it is always best to consult with the wise.....
To make a shidduch is a GREAT mitzva. To break one up can be an even greater one.