>>81793489 (OP)It depends on a few things, like whether you already knew she had a boyfriend, whether you have feelings for her, etc.
But if she accepted without really thinking twice, and she actually enjoyed it, I think it's her fault, a person who destroys a relationship is the same person who is in the relationship.
*Milk sip*
Sooo
In short, it's her fault... Or at least you're not telling us something.