A house was bought during marriage but my name was left out. Am I still entitled to half in a divorce?

This is not a yes or no situation there may be some co-ownership but probably not 50-50. You need to contact a lawyer asap.

The key is the source of the funds used in acquisition- were they from a separate source or community? This would include mortgage payments.

You are entitled to one half of all assets acquired during marriage except gifts or inheritances. Get a lawyer to protect you on this issue.

Your wife's portion of the house is community property, unless your wife used separate property funds (such as inheritance or premarital savings) to purchase the property and make the payments, or if you entered into a transmutation agreement (the agreement would use those words). If she used her savings that came from her earnings during the marriage, and makes the payment using her earnings, then it is presumed to be community property. Your name on title is not needed. Your mother in law's interest would remain hers. The court can hold a hearing to determine their ownership shares.

You may have an interest in the house for part of the principal paydown and a corresponding percentage of the appreciation.