I am 21 years old and my boyfriend is also 21 years old. We are very much in love with each other. We have been together with each other for more than 3 years now.

My mother came to know about our relationship recently. She is against our relationship. She has one problem and that is caste. He is a Buddhist and I am a Hindu Bhandari(Marathi). She has told me to forget him or else she'il lose her temper and may do anything to herself. Please tell me what should I do because I love my boyfriend a lot. She has only one problem that caste.

Please give me some suggestion

Ignore your mother and stay with boyfriend. Your real issue is that you must have been ashamed of him, since you never told parents about him for 3 years, so I suspect you knew this was going to happen, so in 3 years what were you expecting to happen?

Ignore your mother and stay with boyfriend. your real issue is that you must have been ashamed of him, since you never told parents about him for 3 years, so I suspect you knew this was going to happen, so in 3 years what were you expecting to happen?

No
I am not ashamed of my boyfriend.I didn't tell my parents because I knew that having a relationship won't be accepted in our family.My mother said to me that we won't allow you to continue.She said if he wasn't a Buddhist then we could have thought about your marriage.please tell me how should I convince her.
Right now I am still studying.I can't even back answer to my mom at this particular time as today I am nothing.
Please tell me what should I do

You should keep studying and be able to support yourself without your parents and marry of your own choice. Everything was fine while it was a secret, but you knew someday the secret would be out. You also knew your mom wouldn't like it and would threaten anything to prevent you from going down this path. That would have been the time to plan for the day of reckoning with your parents and be prepared to stand your ground.

You may never convince her, but you can try, by going along with what she says and doing what you have to when you are away from her. Where is your father in this?

My father is not knowing about as my mom has not told him about that.
She didn't tell my dad to avoid something serious from happening and has warned that if I still meet my boyfriend then she will tell my dad.
I don't know how my dad would react as sometimes he's very cool with things,sometimes he is strict

You should keep studing and be able to support yourself without your parents and marry of your own choice. Everything was fine while it was a secret, but you knew someday the secret would be out. You also knew your mom wouldn't like it and would threaten anything to prevent you from going down this path. That would have been the time to plan for the day of reckoning with your parents and be prepared to stand your ground.

You may never convince her, but you can try, by going along with what she says and doing what you have to when you are away from her. Where is your father in this?

Given that your culture is so built on having parental consent I would not rock the boat while so dependent on parents for everything including school. That means the idea of marriage is on hold until you have reached that point of indepence you can make choices for yourself, as there seems to be no convincing arguments that don't bring drama and conflict and hard feelings of resentments with it.

If you had spent this time exploring WHY your parents have this prejudice and love of tradition, then maybe understanding would temper your actions, and maybe you could have kept your secret and be discreet until a better time. A time you could have better stood for yourselves as responsible independent adults who wished to follow their own path, no matter the wishes or influence of the parents.

I think it's a bad idea to openly defy your parents unless you are prepared to pay the consequences. So just keep planning for your own future, and be ready when the time is right.

Obviously that's not now, and there are no quick easy fixes to change that fact.