Hmm. How about getting a 6-12' boat and learning to sail with the local kids or on a lake or wherever there is suitable water? Racing against them will teach you how to sail, as well as providing instant feedback on how you are doing. You might then try 20-30' or better local boaties are always looking for reliable crew who know the basics.
Hopefully you will always respect the sea, but as you acquire knowledge and competence your fear will diminish.
Your wife may change her thinking when four things happen. 1. She sees you becoming competent. 2 She has some pleasant experiences. 3 She becomes confident and competent herself. 4. You don't talk of doing marathons when she knows very well you can't crawl and wisely she would not go round a bay with you on a Hobie.