I think keeping it professional is mostly on the professional's shoulders, but on your part, I think realizing it isn't a reciprocal relationship is a big thing. I mean, you open up a lot to your therapist, but your therapist shouldn't be opening up a lot about their personal life in return. It's one-sided, based on your therapist helping you. Personal, intimate relationships are reciprocal; professional ones, even if they involve a lot of personal information, are more one-sided.

I kind of think of it like an OB/GYN. My OB/GYN has to stick his hand and other instruments up in my vagina on a regular basis. In another context, that would be a ridiculously intimate action. But in this context, I'm not seeing his junk in return, I'm not expecting anything from him except a reasonable standard of care, and it's something we're both doing for my health. We're friendly and make some small talk, but we're both very well aware of why we're there, even if there's a level of trust and vulnerability that doesn't exist in most other interactions with relative strangers.

I think it's easier to draw lines when you're talking about physical vs. psychological issues, but I think the same basic standards apply.