Is your paycheque being directly deposited into this account by your employer? If so, open a new account for yourself and deposit your money there - there is no need to share an account with someone and allow them to spend your money while they are with someone else - how long have you been allowing this? Why is it her money too? I'm not understanding that part? Do you say this because it's a joint account - if so, who cares?
Cutting her off should have been something you did a long time ago if she was with someone else - seriously! Who cares if she won't be happy, time to start respecting yourself on this issue.
If she isn't with you and she's with someone else, why would you continue to support her financially?
Email - not sure I would have emailed her. I would have maybe phoned her on it or texted her, it would be more immediate and you could still do it remotely and not show any emotion.
