Does a girl born on a new moon has to get married to a guy born on new moon too? They say if a girl is born on new moon marries someone born on other days except the new moon, the groom has a shorter life and dies early.
Is there any truth behind this?
There is no truth in it.
Amavasya is condition of Chandra yuti Surya in Jyotish. This means that the Moon and the Sun are at the same degrees.
This also implies that, in the person's chart, Sun and Moon will be in the same Rashi, Nakshatra and Bhava.
This condition is also called as moudhya-Chandra or a combust moon.
It essentially implies that some of the traits that Moon implies in a person's chart will be not so powerful.
The extent of this will again vary from person to person depending your Lagna; the Bhava, Nakshatra and Rashi where the Sun and the Moon are sitting e.g if this combination is happening in Karka Rashi (Cancer) which is a sign ruled by Moon, the effect of moudhya will be lesser.