Rather a curious question. Why do you do this ? You say you are not in love anymore, in a way that implies that neither of you is particularly in love with the other. Why, then, do you feel the need to send her a message announcing your love ? Millions of men who do indeed love their wives, never ever do so. If you move, at some later stage, towards divorce or separation, she would have a sound basis for feeling cheated, for feeling that you lied to her or misled her in this way. If she asking you to provide such reassurances of your love ? Are you sending the SMS rather than face the responsibility of having a serious discussion with her about what's not working well in your relationship ?
Do you actually care about the relationship ? If its fading, without animosity but without much love, but you would like to preserve it, why not suggest to her that you two get involved in marriage counselling ?