It sounds like living with your mom is somewhat of a toxic environment for you. Is there a way for you to find a place of your own? Or with roommates? If your mom has a boyfriend then she's not alone dealing with her MS. That could be a good first step in finding some emotional peace.
I know you said you don't have insurance and that is really tough. However, how about checking out a community clinic. It can take quite a bit of time to get in but they do have counselors and psychiatrist that can help with depression both with therapy and medication.
Also, AA meetings are free and are a good way to get out of the house and meet people when you're not at work. It doesn't hurt to check out a few meetings and see if it's something that might work for you.