Responses
I think it's this
http://www.mangago.me/read-manga/kazoku_ni_narouyo/
And this is the prequel
http://www.mangago.me/read-manga/itsuka_koi_ni_naru_made/
i didn't read this manga very long ago but i can't find it in my lists so any help is appreciated!- here's what i remember
it's a prequel, a group of three childhood friends, two boys, one girl. i remember the girl is called tomoe-chan, maybe tomo? the two boys get together and in the main series, tomo(e) returns, heavily pregnant and leaves the two to raise the child.