All about crabs...?

In the world of relationships I will admit (experientially) I am a bit of a novice but in theory i am actually an expert at matters of the heart (hey aren't we all?) so when someone seeks my advice I feel I come from a place that can truly help them- unbiased and fair and equitable (hell, my dream job from when I was a little girl was I wanted to be a judge back in the day but my law track got derailed) I digress. Bro #2 is having girl issues : what say u?2 years in a committed relationship all is 'we'll' well as in nothing life shattering thank god. A few absentee moments and mis-communications abound but they are trudging along towards... Bliss?  Love? Marriage? kids? all of the above? I guess...
well- a trip came up that she wanted to go on--it was a trip someone from her job was planning to crab fest. Now, it was themed up as a either a singles thing OR something where the girls can go on and have a good time (clubbing/ dancing/ etc). She invited her boyfriend and he really don't have it in his budget + he mentioned that he was not too keen on her going (there was mention of debauchery etc etc) well OK. She put it aside and they planned a trip together (Aww) well fast forward 2 months and lo and behold she 'forgets' to mention that she in fact paid for crab fest and fully intends to go crab feasting and deal with that. The brother was pissed -- not cause of the issue of crabfesting but the general 'perceived' lack of care of his feelings in the matter.
What say me?
i was all well, she paid for it and wants to go and this is not something she has done/ experienced before so why not'? cause i mean really no man (my man or not) is gonna say who what when where and why i can go somewhere or not. yes, I will ask your opinion and take that into consideration- then of course like life I will do the hell WHAT I WANT.
that opinion didn't go over too well- but it is what it is.
what say you?

*update, she didn't go-they continues to argue about the perceived cheating and lack of information sharing and if this is what relationships are-- i don't need em. I still want one.**