Your EX's actions remind me of the OP's of another tread, which oddly enough received many thanks:
http://www.revscene.net/forums/67320...instantly.html.
What's good for the goose, is good for the gander, right?
I don't know why people feel the need to take revenge against ex's, like ending the relationship isn't enough.
I would be completely upfront and honest with your current girlfriend. You're both mature adults, so she should understand that the ex's actions are completely out of your control and not hold it against you. I'm sure your gf will find the situation frustrating, but unless things escalate even further I don't think it will jeopardize the relationship.