My bf(20M) is emotionally unavailable for me(19F)

We have been in a relationship for almost 4 years now and I'm very grateful for him. I thought i could share anything with him and he'll always be there to listen. We have our 12th boards going rn. I've been in a havoc because of his behaviour towards me. He lost his grandmother a month ago and still grieves her loss. She loved him alot and he misses her alot when he goes in his "dadi"ghar. He shares with me how he's feeling and I always listen to him and comfort him. Recently I've noticed a sudden change in his behaviour towards me. He kinda dry texts me or doesn't text me at all or when we are on call and I get goofy he doesn't match the vibe and gives me straight up answers in a rude tone. I would have understood his behaviour if he didn't show the duality of it. We sexted whole night a few days ago and he's been pretty active in groupchats he's usually the one who initiates conversations and send memes and joke there. When i tell him something I wanna do or send him memes he says "padhle thoda pehle". He has always been very soft spoken to me and he is that way in general. I don't understand his sudden change in behaviour. I talked to him about it. He said he's sorry he can't be the same he's having a hard time rn he can't give me time and listen to me. I would have understood his behaviour but then why is he fine sexting me or fine planning meetups in groupchats. I told him I want to breakup nothing's same inbetween us anymore. He called me selfish and that I don't understand him . He also called be ambitionless for thinking of all this instead of focusing on studying and that pin pricked my heart as someone who used to be a straight A student. By the end of the conversation i apologized I felt it was my fault. I feel so stupid, guilty and enraged at the same time.