I'm so sorry to hear about this. I'm sure that you are livid. If he signed your name to the checks he can be charged with forgery. Have you talked to the people at the bank about how to handle this? Makes you realize that you just have to keep everything under lock and key.
It's things like this that make me realize that there is just no dealing with someone in addiction. It's hard enough to deal with someone that is sober.
My heart is going out to you. Vent here all that you need and use your calm to take care of you and do what needs to be done.
Stay safe!