I don't think anyone else can really say whether or not he's done anything wrong, because we aren't in your relationship. Each relationship has it's own set of rules regarding money.
Surely you two must have talked about finances at some point, if you're planning on getting married soon? If you haven't then you need to sit down and have that conversation as soon as possible. You need to decide how stuff like this is going to work in your marriage. Not talking about it is the worst thing you can do.
In my marriage this would be considered a huge betrayal. We are always totally transparent with money and we share everything. Some people think this is crazy, but it works for us. The key point is that we discussed it and decided between us that we wanted to share everything. So, if I found out my husband had 60k hidden away, that would be a huge betrayal of trust, because we've explicitly agreed not to do things like that.
In your case, if you haven't talked about money before, and you haven't agreed that you have to tell each other about these sorts of things, then I don't think you have a leg to stand on.
Bottom line here is that you need to sit down and talk about money before you get married. It's essential.