I can't decide if I am being over sensitive or not.
DH was invited on a stag of a guy he knows more of an associate than a friend they work in the same field. Would text occasionally but have never been out for a drink or done anything 'friends' would do. Anyway I didn't mind him going on the four day stag to Spain 
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We were also invited to the wedding but it clashes with an important family get together on my side (religious) and our sons birthday weekend. His birthday is the Friday, my family get together on the Saturday, sons bday party on the Sunday. So we decided that we wouldn't go to the wedding as they aren't really friends. DH was fine with that as he didn't want to go to the wedding anyway.
I've told sister we will be at the family get together. So off he goes on the stag and the other lads there work in the same field as DH. I barely heard from him while he was away which annoyed me a bit as I was at home juggling childcare and work. He comes back on Monday and yesterday said that he would he going to the wedding now as he really got on with the boys on the stag. I have told him that we have already made plans and it's rude to go back on those just because he has made a group of new friends. He thinks I'm being unreasonable.
- he always does this meets a group of new people and puts so much effort into them and will choose to do things with them over his family until the novelty wears off
- sons bday party is early on the Sunday so he will have a hangover and be grumpy while I do all the party organising
Aibu to dig my heels in and tell him we have to stick to our original family plans