Don’t know what else she is hiding!

A few weeks ago, my partner was away, and I happened to look through her closet. She had a stack of photographs with a guy I had never seen. When she returned, I confronted her, and she was shocked. Apparently, this was someone she had dated before she met me and had decided not to tell me about it because she had been engaged to him for almost a year. I didn’t know how to react because I thought it was something she should have shared with me. We have been together for two years and I didn’t even know she was once engaged. She has apologised for not saying anything earlier, but I am worried because if she can keep such a huge secret from me, I don’t know if this is a person I really know anymore. Am I reading too much into this? Should I just put it behind me and move on with her?
That depends upon how much you trust her and how you both communicate, going forward. If she withheld this information from you, she must have pretty good reasons, which is what you should focus on because it has implications for your future together. You are both entitled to decide what you want to share with each other because your personal lives are your own, but if this starts to create a sense of distrust, it can grow to overwhelm your relationship. I suggest airing your concerns as soon as possible, so she can come clean and give you an honest explanation for why she didn’t talk about this. Tell her how you feel about the secret and what you are worried about. This needn’t become an issue if you are both committed to fixing it. 

My girlfriend wants me to be more loving and caring, but I am doing everything I can and don’t know what she wants from me.
Why not try asking her for specifics? You may be doing everything you can, but she obviously doesn’t see it.