I agree with Victor.
It sounds as if you have found a lovely girl who cares for you, but you could lose her.
Trust is extremely important in a relationship, and she has given you no reason to doubt her. You have some issues from the past. Deal with them so that they don't affect the present & the future. Get some counselling if you can.
And remember, teenage years are difficult. You are a young man, but you have, so far, only had the experience of being a child or teenager. It's all a learning experience. Stop being so hard on your girlfriend and yourself. Enjoy yourselves and be happy that you have found a nice girl, who you care for & who cares for you.