Yes, it is.

Here’s simplifying what the law in India says. A man is said to commit rape if he has: 

1. Sexual intercourse with a woman without her consent or with her consent under pressure
2. She’s not 18 but gives her consent for sex when she is unable to understand the consequences 

Rape is a punishable crime and you should take a stand for yourself. Talk to your boyfriend about this and make sure he understands this seriously. If he doesn’t, he’s certainly not worth your time and you should walk away. Always remember, consent is crucial. Sex is your right and so is saying ‘no’.

Also, just to be on the safe side, get yourself tested for any STIs and STDs. His crime should not be your punishment.