My sister is staying with us for a month. . .My boyfriend is not happy! Advice wanted. .

Hello everyone. My sister is pregnant. She is 20, and I am 23 going on 24 this year. My boyfriend and I have been in a relationship for three years (almost four), and we have lived together for the last two years. We stay in a one bedroom apartment. My sister lives with my mom, my other sister, stepdad, and my other sisters two children. My sisters have not been getting along, and I am the oldest. So, I tried to resolve the problem by letting my sister stay with us for one month. My boyfriend is pissed about this, and said that I am a sucker/simp for allowing this. It hurts me. He said my family tries to use me because I am too nice. But, they have never used me, and this is the first time a family member of mine has had to live with us. I am pissed. And while I understand where he is coming from, I feel like I am not getting the same treatment. I get that he likes his alone time, and that this is a lot. But, it is also only for one month. And, she has only been here for 2 days. He said he is going to get a hotel for a week (which I doubt, he was only saying that because he is upset). But, this is my family. I love them both. Why is he giving me a hard time? I just wanted to give my sister a break. Her belly is showing, and she has a one year old son who will be two in October. The father is not around either. I am not allowing her to move in, I am only allowing her to get a break from stress. While she is carrying. I don't want my relationship to take a hit. Like, what if this happens in the future? Idk. Please give me advice, and let me know what you think, and if you have dealt with this before in your own relationships.