Apparently these are called litotes...

...but I prefer to think of them as "I don't want to date you. Please refrain from calling me" statements.

"I don't dislike you." means I don't like you.
"I don't not want to be with you." means I really don't like you.
"I don't not love you" means I have taken a restraining order out against you.

More examples
Litotes: As a means of saying:
"That does not surprise me." means "That is to be expected."
"The food was not bad." means "The food was acceptable/good (depending in emphasis)."
"That was no big deal." means "That was nothing."
"Don't fail me now!" means "Help me!"


Have a great day people.