If your ex tells you that they don't go backwards and you still want to express your feelings about wanting to get back together, it's important to approach the situation with respect and understanding. Here's a thoughtful and respectful response you can consider:
"Thank you for being honest with me about not wanting to go backwards. I understand and respect your decision. I just wanted to be honest with you about my feelings because our time together meant a lot to me, and I value what we had. However, I also understand that moving forward is essential for both of us.
Regardless of what happens, I want you to know that I will always cherish the good memories we shared, and I wish you all the happiness and fulfillment in your life. If you ever change your mind or if circumstances change, feel free to reach out to me. But for now, I want both of us to focus on our individual growth and happiness.
Thank you for the time we had together, and I'll always be here if you need a friend. Take care."
Remember to maintain your dignity and self-respect during this conversation. Sometimes, people need space and time to sort out their feelings, and pressuring them into getting back together may not be the best approach. It's important to give them the freedom to make their decisions while respecting their boundaries.