I think the point here is obvious, its not about growing boobs as muchas it is about lack of communication. Massive list of secrets because you've been unable to talk about your kinks is a burden. Its none of my business, but how old are you? Because to me this sounds like a typical issue of many older guys.
In a relationship, communication is the key to everything. How can you build love and trust to someone if you don't really even know them? Having some topics which are off limits with spouses is one thing, I guess that happens to almost any one, but its not the same as keeping a huge list of things as a secret. Like how I have certain kinks I will not discuss here and not even with my partners as I know they're not into the same stuff. I think that's totally fine, its about preferences.
What I've learned in life, especially last around five years is that openness and communication makes massive leaps in making life better. Believe me I've done a lot of very difficult discussions and "confessed" so much, starting from who and what I am, my transition needs, the fact that I'm polyamorous and its the best way to exist for me, about sexuality and kinks, talking about it all without restrains is difficult at first but its so rewarding. Even if it results into a breakup, too many people stick with incompatible partners and too many can't work around issues which are guaranteed to happen because people aren't simple.
The breast growing thing you have to just explain the way it is. Growing them for fetish reasons shouldn't be seen as something inherintly "evil" immoral bad what ever, its your body and your choices. Maybe you should emphasize how having breasts has made you feel more comfortable in you body? Even when its a kink, it shouldn't be a massive problem to anyone, its not hurting anybody so why bother? Besides there are plenty of men sporting some kind of moobs for plethora of reasons and some have actual boobs too. I think breasts in general should not be sexualised and fetishised at all, there's nothing strange about them, they're a frigging baby feeling fat filled meat sacks hanging on peoples chest, who cares if its a man or a woman because everybody has a fucking chest and nipples and everybody has potential to grow them into a functional baby feeding devices.
Btw, the hypersexualisation and objectification of breasts is largely mens problem. I think men should change their thinking about it, and all chests should be just normal body part which every living human has. Conquering this problem starts in our own lives. I hope your wife understands its not a problem that some guys have boobs, few grow them on purpose and its not hurting anybody.