I don't own Once Upon A Time and never will. No copyright infringement intended.
Mulan should have known better. She hates herself for not realizing earlier this wouldn't end happily for her. And now her heart's broken because the woman she loves is having a baby with someone else (who she also loved at one point, but her love for Philip is nothing compared to what she feels for Aurora).
Joining Robin Hood and his Merry Men is an easy choice for Mulan after Aurora tells her the news. She can't be around her or she's going to burst. It's easier to be away so she doesn't hurt so much.
But it only makes thing worse because now Mulan misses her so much she can't breathe (although that might be because of the rejection; she's honestly not sure). She probably made a mistake, but she needed to be away from Aurora and Philip and their happy life. Mulan won't ruin it for them.
She probably should have made her move sooner, but she was terrified – and she was right to be. Aurora is never going to feel the same way and Mulan needs to accept it.
For now, all Mulan can do is cry when she's alone and wish she hadn't listened to Neal.