This question already has an answer here:
In Westeros it is popular belief that after taking a liking to Lyanna Stark, Prince Rhaegar kidnapped and raped her. However, the belief amongst fans seem to be that:
Lyanna also fell in love with Rhaegar and ran away with him by choice.
I understand that this theory cannot have just been drawn out of the blue but as a non book reader I have seen next to no evidence for this in the show.
So what evidence is there behind this theory?