Have you asked him why he doesn't talk to you? IMO, I wouldn't be kissing someone I couldn't carry on a conversation with, but that's just me. Here's what Mr. Bing Search had to say about this.
Selective mutism is an anxiety disorder in which a person who is normally capable of speech does not speak in specific situations or to specific people. Selective mutism usually co-exists with shyness or social anxiety. People with selective mutism stay silent even when the consequences of their silence include shame, social ostracism or even punishment.
Hope this helps.