My boyfriend's little sister plays matchmaker and he doesn't stop her

My boyfriend and I have been dating for 3 years and 4 months. He has a younger sister who's in form four. Every time his sister comes back from school, he'll get new numbers texting him or Instagram requests from highschoolers, his sister's friends. I've been quiet for a long time because at first I thought it was a child who likes to show off her brother. Plus when we met the sister was in form one. When my boyfriend goes back home to visit his family, he'll come back with new chats of different highschool girls . Another day he came back wearing a chain and I asked him who gifted him. He said it was his sister's friend but it was just a birthday gift I shouldn't be worried,now my problem came where he was wearing the chain 24/7 even when we sleep. I got pissed and asked him to get rid of it. He went on ahead to say I'm getting insecure because of a child, the girl was in form two at the time. I stopped checking his chats for my own piece of kind, but now December when he came back, I noticed he had blocked a new girl on phone book but on WhatsApp she wasn't blocked and it seemed like they used to chat and call alot . After confrontation he said his younger sister uses his phone to text her friends that's why he has blocked the girl after his sister went back to school. Now ,the sister is back this week for midterm. She's in form four now, and yesterday night my boyfriend Bragged another friend of his sister has followed him. I asked him why he keeps allowing his sister to play matchmaker and yet she knows he's in a 3 year relationship. Then he proceeds to say it's not like that, the sister just gives out his number so that she can text her friends using his phone and account, problem is though, he only goes home in December, so why is he getting the follows now in march. Anyway my boyfriend got pissed at me and claimed I love making small issues seem like a mountain. Am I wrong ? Is it normal?

Also forgot to say when he goes back home he always changes how he has saved my name because he doesn't want his parents to find out he's in a relationship apparently they are very strict and we just finished campus a year ago.

Update. I've broken up with him. Thanks guys