I think you should move on from her, don't lose all hope about dating just because this one girl. I know how you're demi-romantic, so I honestly think before you rush into a relationship, get to know that person and bond a bit more so you feel comfortable around her. People learn, and move on from the past. Don't let her drag you down into feeling bad about her and not leaving her. If you don't leave her, you'll be the one feeling jealous and empty each time she tells you how romantic he is with her. So my overall message is to just move on and take that time to build your self-esteem back up. I really hope everything turns out fine for you.