The blood part definitely seems to have been the witch
The once for love bit or possibly even the once for blood could be Tyrion?
either the love part or the blood part could refer to him.
love as in love for his brother/family, or blood as in his blood relations
I doubt he would do it for Gold
After all, most people assume the blood part was the witch, but that happened before that prophecy at the house of undying.
The blood or love part could also refer to Jon in some way. While I do not see Jon betraying her, she could betray him, possibly for love?
The prophecy just says "three treasons will you know" It doesn't necessarily mean they will be done to her