I always ruin a potential relationship with a girl
Why do you feel you keep ruining relationships?
I did some things this year this new girl didn't approve of.
There are a lot of relationship gurus online like on Youtube. They give good advice so maybe you should look into it or else you might always have relationship trouble.
If we really like each other, its fine.
Advice can be really useful, did she tell you why she left? I think if you ask her why you broke up she will give you an honest answer and you can try to improve on that.