Can I include a variable related to the outcome variable into statistical analysis?

Question

My research question is about intra-individual variation, meaning how the variaion in the personal level is associated with other variables. The study population reported their behaviour for three waves. For the dependent variable or the outcome variable, it is the standard deviation calculated based on the three waves. The independent variables included general SES variabels, and I also include the first wave information for each participant. But the problem is that the outcome variable is calculated based on the the three waves, and now the first wave number is included as one of the independent variables. I am not sure whether this is proper. Can anyone help me with this? Thank you!