Why Adichie's Americanah is, at least so far, more than just a teen-romance novel

The 2nd section of Chimamanda Ngozi Adichie's novel Americanah (2013) becomes a teens-in-love story, as we move back a little bit in time and see as Ifemelu, in h.s., meets her first serious boyfriend, Obinze. This part of the story is only somewhat interesting to me and seems, on basis of pure plot, not much more than a teen romance novel; what raises the novel to a higher level and will (or must) keep my interest and has made this novel a sensation rather than another star-crossed lovers story is the cultural context: We get back story on Ifemelu's family - her mother a religious fanatic jumping for church to church and her father an idealist of a sort, dismissed from his government job (in Lagos) because he would not submit to the humiliation of addressing his boss as "Mama" and now out of work, putting family finances in jeopardy. Ifemelu seems to be the only one in her cohort of school friends to be living on the edge of poverty, so on the one hand her eyes are opened by the privileged lives of her classmates, w/ their European vacations etc., and on the other hand for the first time she recognizes the poverty of her own family, e.g., she didn't realize it was unusual to not have a telephone at home. This dialect reminded me of the American novel Prep - scholarship girl in a new environment - though it's clear the Ifemelu fits in well in her new scene, intellectually and socially, and that a love relationship w/ Obinze, from a family of intellectuals and scholars, will only advance her stature (and self-esteem). What everyone in her clique holds in common is a fascination w/ all things American - and we know that this force will drive her to emigrate to the U.S. and to attain success, with the mystery being: Why does she choose to return to Nigeria? She's not trying to reconnect w/ family nor is she on a social mission; is she really expecting to start anew w/ Obinze, who is to all appearances happily married and involved in fatherhood?