My mom always vents to me about what's upsetting her. I love her, but all it does is make me sad. What can I do?

If you feel that you are getting overwhelmed with your mom venting to you about her issues then I would recommend for you to let her know to use other resources such as getting help from a professional therapist. I understand you love your mom and want to be there for her as much as possible, however, it is important for you not to get overwhelmed cause then this can lead to you overwhelming yourself and then end up having chronic stress. Therefore, guide her to get the help she needs. You can even help her look up different locations and resources for her. This will reassure her that you care for her.