Ok, from what I remember, it was a romance manga. The girl was in a relationship and the guy was just being romantic with her. But because of a possibly abusive (don't really remember) ex boyfriend she had, she's insecure about herself and her current relationship. I believe the girl had black hair and the boy was blonde. thanks!

Update: I'm still looking, but it might be Kimi ni Todoke. If it's not, it has a similar art style

Nanoka no Kare kinda sounds similar, though the girl has lighter hair... Sorry if mistaken!