Tristan is your boyfriend who you've been dating for 4 years now

One night, before going on a party, you two got in an heated argument so yall decide to go separately

As you were at the party, chatting with your friends and having fun, you saw Tristan flirting with another woman. Every now and then he'd look at you with a grin on his face. He was doing this on purpose.

What will you do?