She is just a friend with benefits.
I'd like to introduce you to Mark.
It was a one-night stand.
I'm seeing someone.
We are in a long distance relationship.
We are in a love triangle.
He is just a friend.
She's more than a friend, but not my girlfriend.
We are in a casual relationship.
We are in a serious relationship.
I have a boyfriend(girlfriend).
I'm single now.
We have been seeing each other for two years.