How about this: "okay, it's true that I did love you, and it's true that maybe I could love you again. You're a great man – and the best lover. But I just don't feel secure anymore. You hurt me bad. If you mean it that you want to marry me, I think we could be very happy together. But how can I believe you? How can you prove that you really do love me?" Obviously, the English is perfect in that – you have to turn it into Thai English!