He needs to go on the trip. When he asked you earlier to not spend it sounds like it was before his cousin's bereavement. Death changes your perspective on things especially if the person was young.
If you are struggling with his shift in priorities, commitment to his family/ having a large family, I don't think this is the person for you.
My OH is the youngest of 10 siblings, and over the years he has always been helping one or another of them out (usually either financially or with legal matters) and I've just swallowed it, and reminded myself it speaks to his character. I'd rather have a man who values his family than pushes them away for a wife/partner.
Wonderful advisce from others- you could book a trip too, with plenty of time to sort out the wedding.