My boyfriend's mother is claiming that I'm having an affair with her husband.

My boyfriend’s mother (55) recently cornered me and made it clear that she is aware of what she feels is my true character. I’m a 26-year-old woman and have been in a relationship with my boyfriend (25) for about a year. We’ve started discussing our future together, including the possibility of settling down, but I am an immigrant in the United States while he is a citizen and a military veteran. Currently, we both live with our parents. Sometimes I stay at his house, and other times he stays over at mine. I live only with my mother (48), who is fine with my boyfriend visiting. In contrast, my boyfriend resides with his mother, stepfather (50), and his two younger siblings. From the start of our relationship, my boyfriend warned me about his mother. After his stepfather cheated on her, she installed cameras throughout the house, which reveals her insecurities and controlling behavior. Recently, she accused me of trying to use her son to obtain American citizenship. She claimed to have videotapes of me entering her husband's room and suggested that I “hacked” her camera system to erase any compromising footage of myself. She stated that her husband would never leave her for me because, in her eyes, I'm just “a nobody,” while she is the love of his life. She went on to say that she would persuade my boyfriend not to marry me and threatened that he would ultimately leave me. Furthermore, she claimed he is aware that I am a “homewrecker” and that he supposedly promised her he would “shoot me in the head” if given the chance. She even attempted to blackmail me into silence about our conversation. Feeling devastated, I left her home, wished her well, and got into my car. I called my boyfriend and told him everything. He confronted his mother and left the house that same night, expressing his desire to distance himself from her. He apologized for her behavior and admitted, “I told you she was crazy, but I didn’t realize she was THIS CRAZY.” The following day, she called him begging for him to come by and talk. He agreed, and even though I’m hurt, I want him to clear the air with her. We have always had a strong relationship, and I trust him. However, I’m feeling sad, broken, and confused about this situation. I sense that his mother may need mental health support, but I worry about potentially becoming the enemy if I suggest it. Her lies, blackmail, threats, and slander have left me shaken, and I'm concerned she might manipulate my boyfriend or retaliate against me if he chooses to return to her. To clarify, everything she accused me of is false. Her husband told her she was mistaken, and both my boyfriend and his older brother (35) defended our relationship, as he also experienced similar treatment from their mother when he married a Central American woman five years ago. In the end, she assured me that if not me, another woman would try to come between her and her husband and sons, but she would fight to prevent that from happening. I would appreciate any advice or insight on how to navigate this difficult situation.