Please suggest me. I am in a very serious problem. I am in love with a guy who is my family friend.?

My Mom is every thing to me. because she is the one who brought me as an engineer.but, she is little bit egoistic and adamant. Now I am 25. I am working in IT firm and My Guy is also in IT firm. We both know each other well for past 7 years. we both are from different caste. Both of our families well known to each other for past 10 years. But in middle, My mom fight with her sister for some money issue. My Guy's parents were with my mom's sister and they tried to convince both the sisters from this quarrel.but, my mom start hating them because of this issue. She is saying that they are third persons and how they can interfere in our family matters. but, they just tried to solve the issue . His parents are intercaste couples. They accepted our love. But, when i told my love to my mom, she started bitterly scolding me like anything. she said i cant let you to marry in other caste, especially to them. She is blackmailing me by saying that she will die. She is very adamant and egoistic. she has some asthma and breathing problems. she cries always and tempting me to do what she thinks. sometimes, she refuses to go to hospital even in worse breathing problem and asks me to do what she thinks. She threatens me by showing my younger sister's life. I am the sole bread-earner for my life. I need to support my family even after my marriage. Since My Guy knows my family situation very well and he supports me in this. He is a only guy in his family. No brothers and sisters to him. He is very supportive to me in all aspects. But my mom, threatens me, she always crying, make her body condition very worse and refuses to go to hospital. I even said her i wont marry him if you not like this marriage. I will see my sister and my brother's life. please leave me alone and dont ask me to marry anyone. But, she is not even hearing me and understand my feel. she is very adamant that her thinking should succeed at any cost.My mom scolds my guy and her family very bitterly. she forces me to marry a person that she selected. I cant marry any other person other than my guy. If my marriage happens with any other guy, definitely I will die. Sometimes I feel like suiciding... But suicide will ruin only my life and my guy's life. i don't know how to convince her.. If I start this matter, she starts crying by saying you cheated me, you are a cheat, etc, etc... I am thinking of my family's wellness only. But, my mom thinks only about her caste and her ego. My sister and brother are not even opening their mouth due to my mom's health. All my family members are against me only because of caste. I don't want to cheat a third person in the name of marriage by killing/hiding my love. Ultimately I don't want or like to marry any other person. Please help me how to handle this situation.