Pls help me find this

So the fl is bff of ml's sister. Both fl and her bff are roommates. I just remember one scene
One day fl and ml were having drinks and when he was about to drop her back to the room he couldn't find the keys, so they went to hotel and ended up having sex. Um idk the part after that but she got pregnant.
Also she works ina company while I think the ml is younger than her (not sure)