For most professionals, it would be against their own ethics to date someone they are working with/for. So, yes, I think you were right at first when you said you would have to sever professional ties with them before dating. Yes, it means you would have to fire your lawyer. But I would discuss the reasons why first. And if they weren't interested, I wouldn't fire them. If you fire them first and then ask them out, they will probably just not want to date someone who just canned them.
Also, you just have to be careful. A lot of professionals are not even thinking about romantic possibilities with their patients/clients/etc. Even approaching this subject with them might be uneasy.
Good luck.
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