Your boyfriend’s mother is over-protective of her son, it’s true. It’s also true that it won’t end well if you confront her. If you know you are truly doing the best you can to find employment, please just let this roll off your back. It doesn’t matter what she thinks. It matters what you and your boyfriend think.
I am concerned that you think your boyfriend isn’t “standing up for you.” Maybe. It may also be that he knows that taking on his mom is a losing proposition and that it’s better just to nod and appear to agree, then go on with what he thinks is best. If that’s the case, take a cue from him. You can’t argue someone like her out of an irrational fear.
Don’t defend, explain or apologize for your situation. Just tell her, “I completely understand why you are worried. I’m doing the best I can.” Then change the subject. If she persists, make as graceful an exit as you can — without anger. Be pleasant. Tell her again that you appreciate that she is worried but that you have to go.
When people go low, the best thing to do, really, is to go high.
I wish you well.