My husband and I sometimes do things with friends separately, but not at the expense of endangering the household financial stability, and not instead of doing things as a family. He recently had the opportunity to go out of state to an event that would be perfect for his area of interest. As soon as he heard about it as a possibility, we talked about it. Once we got the details we learned that it cost much more than we had disposable funds and it wouldn't be possible to make it happen in the time allotted. So he didn't go. Disappointing, yes. But logical, mature, and drama free.
You and your husband seem to have a communication problem. He told his friends a year ago that he would go, but didn't mention it to you until now. That means he was intentionally avoiding a conversation. He knows he is being selfish and immature (whether he would admit it or not) but he still wants what he wants.
Of course you're upset. You should be. You should be telling him, bluntly, that committing something a year ago to other people and hiding it from you for 11 months is not acceptable. He needs to be told that you're disappointed that you don't have vacations together, and you want that to happen first, before any more expensive solo fishing trips.
You shouldn't assume things about what the two of you will do either. Talk openly about what you want and what you need. Discuss couple-vacations ideas as they occur to you.
You need to rock the boat, L.. You've been married for 20 years, but your marriage is not all it should be. There is no place in relationships for secrets and silent assumptions. You have to have the conversations even when it is uncomfortable, hard, or you worry someone might get upset.