Interesting point. The important part is this, though:
No evidence whatsoever.
It is known
that he "stole" her and its pretty likely that he bedded her. When i read about the "bed of blood" for the first time, i actually thought Rhaegar had gone mad and murdered her for unrequited love. It wasn't until later that i saw the hint at childbirth. And the possibility that the unrequited love went another way entirely...
IIRC, we have no idea wether he actually did her any harm, or wether she loved him. All we know is what Robert
claims he did, but there are several things that make me doubt his story:
1. Robert wasn't there. He only knows whatever Ned or Howland Reed told him.
2. Robert was
madly in love with Lyanna. He started his Rebellion for her, not for the Throne after all, and much of his later decline is attributed to her death. It's entirely possible that he
made up the rape;
--> To bear that she (maybe even voluntarely ?) left him for Rhaegar
--> To deal with her death. This way he has somebody to direct his hate at (raping Rhaegar), rather than having his true love ripped from him by mischance (simply death in childbed)
Keep in mind that this isn't "lying", it's more something he's been telling himself to bear with the truth