In Monday's Daf Yomi the Gemara mentioned the איסור of ונשמרת מכל דבר רע which we learn from that passuk that we're not allowed to look at women in order to enjoy. I was wondering to myself what's the differnece between this איסור and what we learn from  לא תתורו אחרי לבבכם which is mention in ברכות יב:. So I looked into it and found that the סמ"ק (מצווה ל') and also the שערי תשובה (שער ג' אות מ') both say that the איסור of לא תתורו is only if one is planning about sinning with that woman that he is looking at, similiar to the איסור of לא תתורו of עבודה זרה where the sin is only if one us planning on worshupping idols. This idea I also so very clearly in the ספר חסידים and the אגרות משה (אבן העזר א ס"ט) also explains the difference between these two sins in that way. לא תתורו is only when one is planning on sinning with a woman whereas ונשמרת מכל דבר רע is only by looking at a woman in order to enjoy even if not planning on sinning with that woman. This sin is because it will cause you become טמא via קרי.

The thing is that I recalled the משנה ברורה (סימן ע"ה ס"ק ז') quoting the passuk of לא תתורו regarding looking at the finger of a woman in order to enjoy (also the חכמת אדם brought that passuk). Where that statement in the gemarah was mentioned about the passuk of ונשמרת מכל דבר רע.
Anyway, it sounds like there's a מחלוקת on how to interpert the איסור learnt from ולא תתורו. According to the sources I quoted above it sounds like one is not considered עובר on לא תתורו as long as he isn't planning on sinning with the woman (whereas he is עובר on ונשמרת מכל דבר רע). But according to the משנה ברורה you're also עובר on לא תתורו by only looking. Does anyone know any sources from the ראשונים where it's stated more clearly the opinion that the משנה ברורה brings?

Also I was thinking according to this opinion, what is the difference between the two different איסורים?
One possibility that I thought of is that לא תתורו is the איסור regarding the act itself, whereas ונשמרת מכל דבר רע is the איסור regarding the outcome.
Or maybe it's possible that they are both the same איסור from to differnet passukim?
Would love to hear if anyone has any more clear sources on this.