To vibe with someone means to talk, chill, hug, kiss etc. and act as a couple without claiming each other as boyfriend
yet. You can be open, and share your feelings with each other, you can have fun together, be there for one another.. go places together and still be okay with the fact you're not technically committed
Person 1: Yo, you think Liz and Ez are going out? They're always together.
Person 2: Nah, they're just vibing man. They might end up together though, who knows.
Person 1: Damn man, I just wanna vibe with someone too.