It sounds like you’re in a tough spot, and I understand how important it is to reassure your girlfriend of your feelings for her. Here are some steps you can take to help convince her that she is the only person you are attracted to:

1. Open a Heartfelt Dialogue:

Start by having an open and honest conversation with her. Choose a calm moment when you both can talk without distractions. You might say something like:

"I really want to talk about how you feel. I understand that my reaction made you doubt my feelings, and I want you to know how much I truly care about you."

2. Acknowledge Her Feelings:

It's essential to validate her feelings. Let her know that you understand why she might feel insecure, especially given your past. You can say:

"I can see why you might think that, especially considering my past mistakes. I appreciate you bringing this up, and I want to clarify things."

3. Reassure Her of Your Commitment:

Make it clear that your feelings for her have only grown stronger over the years. You could express your feelings with something like:

"You are the one I want to be with, and I love you for who you are. My past is just that—my past. You are my present and my future."

4. Be Transparent About Your Past:

Sometimes, sharing more about your past can help alleviate concerns. You might explain your relationship with your high school fling, emphasizing that it was never serious and doesn’t compare to what you have with her. You could say:

"My 'ex' was just a fleeting moment in my life. I realize now that it was nothing compared to the love we share. You mean so much more to me."

5. Show Affection Regularly:

Actions often speak louder than words. Make a conscious effort to show your affection and appreciation for her daily. Small gestures like:

• Complimenting her genuinely.
• Planning a special date night.
• Leaving sweet notes for her to find.

These can reinforce that you are focused on her and your relationship.

6. Encourage Her to Share Her Concerns:

Invite her to share her feelings and insecurities without fear of judgment. This can help her feel more secure in the relationship. You might say:

"I want to hear what you're feeling. It's important to me that we can share our insecurities openly."

7. Build Trust Gradually:

Since trust has been an issue in the past, it’s crucial to be consistent. Keep your promises and be honest in all your dealings. Trust is built over time, so patience is key.

8. Consider Seeking Help:

If she continues to struggle with feelings of insecurity, consider suggesting couples counseling. A professional can help both of you navigate these feelings more effectively.

Ultimately, your goal is to create a safe space where she feels valued and loved. With time, patience, and open communication, you can help her see that she is the only person you are truly attracted to.

Remember, actions often speak louder than words, so consistently demonstrate your commitment to her. Good luck!