Welcome aboard. You've definitely arrived at the right place to discuss this; unfortunately there are no easy answers, though perhaps we can offer some suggestions. Certainly my immediate thought is to wonder about the quality of your marriage if a boy can get into your heart so comprehensively? If your relationship with your wife is strong, then it would seem likely that he wouldn't have taken over so easily. Working on that relationship is likely to be a constructive way forward.

The other line of argument is that it reflects issues from your past coming to haunt you; unresolved things from your own childhood that he is causing to resonate for you. If so then they probably need working on as otherwise you'll struggle with this issue for the foreseeable future.

As a practical step, trying to get other boys involved in your life may reduce the significance that he has for you, as well as reducing the prospect of anything going drastically wrong.

Does any of that make sense? As I say, you've certainly come to the right place to talk about the issue, and realise that you aren't alone in facing it, which is a good start! And perhaps others here will be able to speak more directly to your experience...