I think you need to be very careful how you word what you say to him, otherwise it could lead to further problems.
Be aware of your tone and don't say it in an accusatory tone.
I actually don't think him going away with his friend is an issue... And when you told him you didn't want to go, he was perfectly at liberty to make plans to go with a friend.
Put things into perspective and realise this is just one holiday. There is always next year and many years to come.
I went on a holiday with my sisters one year and it meant I didn't have money to contribute to a big family holiday that year. I don't believe that makes me selfish, it doesn't mean my sisters are more important than my DH and DC.
We've since been on many other holidays as a family, when I wasn't stretched financially.
It's always worth seeing any situation from the other person's point of view.
I'd also add that you will struggle to convince him of how money should be managed or split or what is fair when he's the C.I.E (chief income earner), I've been there and done that.