Ronaiah Tuiasosopo -- Crushing Social Pressure Drove Him Into 'Fantasy World'

Ronaiah Tuiasosopo -- the man behind the Manti Te'o hoax -- is telling friends he felt compelled to create a "fantasy world" for himself because he felt crushing social pressure from 3 major forces in his life ... TMZ has learned.

We already know Ronaiah thinks he might be gay because he fell in love with Manti while pretending to be the fictional "Lennay Kekua" ... and told Dr. Phil he's "confused" about his sexuality.

But sources close to Ronaiah tell TMZ ... he was always afraid to explore his sexuality fearing scorn and ridicule from the Samoan community, his church community and the football community. At an early age, we're told Ronaiah created a private world for himself, that was not rooted in reality.

Besides playing high school football, Ronaiah's family is a VERY football-centric group -- with several members having played in the NFL.

Instead, we're told Ronaiah created a female character, like Lennay, to interact with men through her ... because instead of feeling guilt about his sexuality, he could chalk it all up to make-believe.