Sharing Our Innermost Thoughts

I recently shifted to a new place with two of my friends. I have known the two of them since sometime now.
They hosted a party while I was not at home and have been hanging out together. They do not include me in their interactions and are super cold towards me. I recently got to know from another mutual friend that one of my flatmates has been bad mouthing me. I want to confront them, but I don’t know how to approach the issue…