Your boyfriend is experiencing a physical problem, a psychological problem, or a mix of both. And problems like those don't resolve themselves on their own.
For as long as he refuses to see a doctor, his health issue is not going to get better. And he knows this. My guess is that he's apprehensive to see a doctor because he's scared of what the doctor will tell him. He's not thinking about how much his impotence is impacting you or your relationship. He's only thinking about hearing some kind of bad news.
Because this is the case, there really isn't much you can do to get him to make an appointment with a urologist and/or a psychologist. He's going to go if and only if he's ready to. But I would recommend telling him how his problem makes you feel. Tell him that you're not angry at him, but this is an issue that is creating distance between the two of you. Tell him that you know that seeing a doctor is hard, but you would like him to do it.
What he does after that conversation is entirely up to him. But hopefully he'll do the smart thing both for his health and the health of your relationship.