聯係 if you

1) Care for him as a friend. He may need your help in some sort of non-relationship matter.
2) Miss him and are willing to fall again.
3) He has never played the same trick on you.
4) This is the only way of your communication. No mutual friends. No third party to contact, etc.

不聯係 if you
1) Concern more about hurting youself if he tricks you.
2) He has played this kind of tricks before.
3) You don't really want to see him again.