With my job I’ve have had a lot of exams to complete over the last three years to become chartered. I started work with two other people, let’s call them Megan and David. None of us live on the town where we work as we pretty much work from home most of the time but me and Megan live on the same town. We finished our final exam this summer and have all passed so Megan suggested we all go out for drinks to celebrate. David said it sounds good but it would be hard for him to get to us as he doesn’t live near us so just said for me and Megan to go if we wanted. Megan suggested then inviting our partners along and I agreed. Megan's boyfriends messaged me to thank me for the invite but mentioned he was going away for work for a few weeks so just to meet up without him. When I invited my gf she said she doesn't want to go but that I shouldn't be going out for drinks with a woman on my own. I pointed out we'll only be on our own because she's refusing to go so she doesn't get to stop me celebrating finally finishing exams. She just said I was being disrespectful and that I should be cancelling. AITAH for not cancelling drinks with a colleague?