Boyfriend went on holiday with female friend

Please talk me down because I am about to go off

So we have been together for over 6 months and from the start I knew that he is very adventurous and never plans his holidays. He hasn't been taking the lockdown well and could not wait to get back to normal life

We're in London and recently flights have started back up and people are allowed to go on holiday. Great news right?

We were gonna go on holiday together soon but I can't get time off work yet, however he has run into his female friend while she was on her way to the airport to go on holiday. They started talking and she invited him to come with her

So he did! He booked the flight, went home to pack and met her at the airport

He texted me to let me know. I haven't responded yet because I'm fuming and might say something I regret. Like you couldn't ask me if I was okay with that? I know damn well he wouldn't be okay with me going on holiday with a male friend!!!!! Who does that?

Please give advice. I've never been in a situation like this so I'm lost