Why can't you take him out for a walk? You probably shouldn't have a dog if you don't have time for walks at least 30 minutes twice a day. But, you asked for help so I'll give it a shot:
You have to get over being scared of dogs first off. Keep in mind that as a puppy, your dog is incapable of aggression or initiating an attack. He does sense your indecision and since he looks to you and your boyfriend for direction, you're confusing him. Act assertive (not mean or rough). Next, BE CONSISTANT. Do you know his signal for when he needs to potty? Watch him like a hawk and when you think he might be ready to go, which will be about 15 minutes after a meal or heavy play, keep him in/close to the area you want him to use. When he does go where you want him to, praise the living daylights out of him while saying "good potty!" or your choice of phrase. Eventually he should learn that that particular area of the flat is 'his' spot and will go there. But, once you make a spot his, you cannot easily change it.
Good luck!
