Are my concerns about my girlfriend’s past justified? She has been in many relationships before, and I am relatively inexperienced by comparison. I know she loves me, and we have been together for almost a year, but whenever we have a fight, I can’t help wondering if she is being manipulative. She knows more about relationships than I do, and I feel insecure because I know she can leave me and be with someone else if this doesn’t work for her. I am always frightened by that possibility because I love her very much and don’t want to lose her. At the same time, that fear is making me pretend to be someone I am not. How do I change my attitude?
It’s great that you acknowledge the need for your attitude to change, given that your girlfriend isn’t doing anything to exacerbate this sense of insecurity. To focus on her past does her a disservice because it implies that she isn’t with you for the right reasons. If you love her and don’t want to lose her, the focus should be on strengthening this relationship and becoming more adept at understanding her. If she is more emotionally mature, you should use this relationship to become a better version of yourself instead of belittling her for understanding relationships better than you. If someone wants to leave you, they will, but you have an opportunity to try and become a better partner because you are lucky enough to be with someone who is more capable of managing emotions than you are. Start thinking of this as a blessing instead of something negative, and the nature of your relationship will change for the better.

Are public displays of affection inappropriate? My boyfriend doesn’t even like it if I hold his hand.
You alone can define the boundaries of what is or isn’t appropriate. If he can’t handle you holding his hand, the problem is his and not yours. Ask him where this fear is coming from instead of questioning yourself.