<human>: Hey reddit,

So as the title states, my SO is vehemently opposed to me having a joint graduation with a girl in our friend group. The original plan was for me and my friend (18F) to share a party because A) it would allow me to financially and logistically have a graduation party (my family couldn't really have one by ourselves) but B) because we were almost set on attending the same college (and her older brother goes to the college so we bond over that and the graduation party would be "themed" to celebrate that). However, she is going to a different school that is coincidentally the rival institution, so we thought it would still be a fun way to bring together our shared and different friend groups in a fun/jokingly competitive environment (with regards to theme we would have it split between the two schools out of jest). 

However, my SO is very against it, saying it is weird and she got very angry when she heard about the plan. She thinks our friend is too flirtatious but my relationship with her is one billion percent platonic (in our close group of friends, if anything ever happened we would all know--we have a lot of trust and transparency). I thought that the graduation party would be very fun but I don't know how to do it without angering my SO. It's gotten to the point where my SO has decided not to invite our friend to her private graduation party at her lake house (not sure if these two things are related but I feel bad because it seems as if she is blatantly excluding her now).

Can you condense the text into three sentences or less?
<bot>: my girlfriend thinks it's weird for me to have a joint graduation party with someone in our friend group. What to do? Is it weird?