Legal Question in Criminal Law in Texas

You have posted this question under criminal law but you seem to be asking a civil law question about liability for damanges.

With regard to criminal liability, technically you could be charged with possession and delivery of marijuana. But the only proof is the word of your roommate. It is HIGHLY unlikely that the police or state would ever take charges in such a situation.

For civil purposes and this is an educated guess because I left law school many years ago & I do not really keep up with civil law - probably would not be any lawyers who would take the case on your roommate's behalf because he would have to make a claim that includes an admission that he participated in criminal activities willingly by smoking the dope. In addition, damages are assigned in percentages of responsibility meaning that a jury could find that you were 10% responsible (or some other ratio) for giving him bad dope but he was 90% responsible for the damages because he made the decision to smoke dope. In that example, you would owe nothing because you were not 51% or more responsible.