Rig Veda III.7.4 says
mahi tvāṣṭramūrjayantīrajuryaṃ stabhūyamānaṃ vahato vahanti | vyaṅghebhirdidyutānaḥ sadhastha ekāmiva rodasī ā viveśa ||
Translation of H.H. Wilson is as follows:
The flowing rivers invigorating him, bear along the great son of TWASTHRI, the undecaying upholder (of the world) radiant with various forms in the vicinity (of the firmmament): AGNI is associated with heaven and earth, as (a husband with) only one wife.
It appears that monogamy or eka patni vrat, which was practiced by Sri Rama, has roots in Vedic Culture.
Am I right?