Let them be for a while

If you partner breaks up with you, it's a horrible experience and can be very difficult emotionally.
Never assume that they are not going through the same torment and questioning their decision to break up.
Most often, they are being coached by a friend.
Let them know that they are special and that you still love them. Point out the best of times that you experienced together.
Then, let them go.
They will come back only if you appear strong and desireable to others. Don't think for a second that they are off and running. They are missing you too.