Regarding doctors, they can always date former patients, and the speciality does matter. Dating someone who treated you for Acid Reflux is not looked at the same as dating your shrink or GYN.
Longtime lurker, but as a doctor in training myself, I just had to comment on this. I don't know who told you that a doctors can "always date former patients", since no one has ever told me (or my colleagues) that. Now, if you're just discussing legalities, then in most states, the only type of doctor who is legally forbidden from dating former patients are psychiatrists. So, in that case, specialty does matter. But most doctors I know would never think of dating even former patients. That doesn't mean it never happens, of course, and I know of a doctor who did have that reputation, of using his position to get dates, and he was NOT looked at as a good doctor by his colleagues. In general, the concept is that even if a doctor is no longer treating the patient, there still exists a power differential, because the patient is used to looking at the doctor as someone who is in a position to care for them, help them, etc. So the relationship is inherently unequal.
Now some of this, I admit, is from self-protection, as there have been cases of patients getting into sexual relationships with doctors, having the relationship end badly, then suing the doctor, even if, say, the doctor only saw the person as a patient once for a 15 minute urgent visit in the ED, years before they started dating. Personally, I would never dream of pursuing a relationship with a former patient. Even without the threat of being sued down the line, I know I would always wonder if the person liked me for me, or from some weird transference reaction.
Now, I think this kind of sensitivity to a dating relationship being "unequal" is rather new, and it used to be much more socially acceptable for a doctor-patient relationship to turn into a dating one, especially since most doctors used to be men, and hence most of the relationships involved female patients, and traditionally, men and women were considered to be unequal anyway. Much like relationships between professors/teachers and students, these are pretty much universally frowned upon today, but I know a number of happily married older couples who met as teacher-student, all with the husband having been in the teacher role, and I recently read an obituary for a former professor in a alum magazine where it was specified that he was survived by his "wife and former student, Mrs. Professor". I actually had heard that rumor about the professor before, but it was still weird that the alum mag found the obit fit to print.
Now, if you're still reading, that doesn't mean it's "wrong" to have a crush on your doctor, this is very common actually, it's just that it would be wrong (IMHO) for your doctor to reciprocate. I would like you to ask yourself, and be honest, would you feel the same way about this guy if you'd met him at church, or through friends, or in some other setting, not in the doctor's office? If your answer is "no" or "not sure", that really is the reason dating the man would not be recommended. I also would wonder if your ideal man is someone who you'd see as superior to you in some way, whether because of intelligence, life experience, maturity, etc? I don't think that's exactly "wrong", either, indeed you could argue that the whole traditional expectation of "Biblical submission" encourages wives to look at husbands as superior in at least some aspects. But it might explain why you tend not to find most men attractive, if you're looking for a superior, not an equal.