Responses
This is probably not it, but your description reminded me of this one, so am sending it just in case!
http://www.mangago.zone/read-manga/hatsukoi_no_atosaki/ (in this one they didn't start a cafe together, but used to create and taste-test different coffees together, and one of them later opened a cafe)
I hope someone sends the correct one, as I'm curious about it too!
The cafe owner built the cafe with ex-boyfriend back then but now he's the only one managing it since they broke up. He's ex-boyfriend suddenly showed up and ordered the cafe .. Thats only part i can remember..