I want to break up: I don't want people to mistake your half-year-old sister for my daughter right after we get married

(From a reader submission, images in this article are from the internet)
Let's break up, I don't want people to think your half-year-old sister is my daughter right after we get married
No matter how beautiful love is, it will be worn away bit by bit in the face of reality. I used to be immersed in love, unable to extricate myself. Dating and marriage are two different things. Dating is a matter between two people, while marriage is a matter between two families. When my love truly faced the test of reality, I chose to face reality and make the most long-term plans. I don't know whether my choice is right or wrong. Maybe I just don't have enough courage to face this test.
My boyfriend and I met in college. He was a senior I met during a competition. I was very impressed by his comments on my speech, and because of those comments I developed a good impression of this guy. Through getting to know him better, I found that he was a very hardworking and ambitious boy. In order to get closer to him, I tried quite a few ways. I would deliberately find out where he was, and then pretend to run into him by chance. Later, after more contact, we became good friends. In order to take our relationship further, I took the initiative to break through the barrier of friendship and pursued him relentlessly. The saying that a woman chasing a man is like chasing through a thin veil was perfectly embodied in me. Not long after, he and I got together.
My boyfriend's family background was ordinary, and my parents were very opposed to us being together. At the time I did not take it seriously. I always felt that the guy I had chosen was so ambitious that he would definitely be a rising prospect in the future. As long as I gave him time, he would definitely be able to prove that he had the ability to make me happy. Just like that, we stayed together and accompanied each other for four years, witnessing each other's growth.
After graduating from college, we were preparing to enter the hall of marriage. When we talked about marriage, my future mother-in-law kept crying poor and refused to pay much bride price. This made my parents very angry. They thought the man's family did not value me much, and that even if I married into the family in the future, I would not have a good life. At the time I also felt somewhat upset. Why was it that I spent so much effort persuading my parents to accept me being with my boyfriend, while my boyfriend's family was unwilling to pay the bride price generously? On my future mother-in-law's birthday, I prepared a red envelope and went to celebrate. At the dinner table, I saw my boyfriend sitting restlessly, going back to the room for a while after eating for a while, and during that time there was also the sound of a child crying. Sensing something was wrong, I followed and looked, and found that there was a half-year-old baby girl in my boyfriend's home. But my boyfriend had never mentioned this child to me. When he saw me at the door, his expression suddenly changed, and he hurriedly explained that she was his sister. I angrily said to my boyfriend: "Let's break up. I don't want people to think your half-year-old sister is my daughter right after we get married." At the time my boyfriend was somewhat at a loss. He explained to me that his mother had given birth not long ago. I could not listen to my boyfriend's words at all and turned around and left.
I think a relationship should not involve concealment, and looking at it from a long-term perspective, in the future this child will definitely need us to support her. Why did he not mention this to me even though we were about to get married, and why was he unwilling to pay the bride price for marriage? What did my boyfriend and his mother take me for? I feel that our love will eventually be defeated by reality, so I decided to give up this relationship. Do you all think I am right to do this?