If I have been common law married for 20 years and all that time we have split all our assets, can i be made to pay alimony?

Alimony no, marital support-- maybe.  Texas is described as an anti-alimony state.  The only way a party can get alimony is if the parties had a written agreement or the both mutually agree in a divorce decree.  Texas, does however, have a similar thing called marital support.  It is granted in very limited circumstances.  One of the times when it can be granted is when the parties have been married for more than 10 years, the receiving spouse does not have the ability to support themselves, and the support cannot be accomplished by a division fo the property.  If you have been splitting assets all these years, that would indicate that your wife has some ability to support herself.  If you are willing to give her more of the marital estate, then she would have extra assets with which to support herself.  Assuming that she can support herself, then you would not have to pay marital support.  The other situation where marital support can be awarded is in cases of physical abuse.  Based on the limited facts in your question, you probably will not have to pay marital support.  However, before you start cranking out agreements and giving away more of your property than you have to, you may want to schedule a consultation with a family law attorney or two in your jurisdiciton.  They can tell you more about the nuances of marital support and give you some input on how your local judges handle similar cases.