Why does my boyfriend think I am immature?

My boyfriend and I have been going out for 10 months. Hes is 23 and I am 19. He is currently building a new house and one day, he asked me if I wanted to write my name and his on the house, but then he decided he didnt want to anymore. I asked him if he ever wrote his name with his previous ex girlfriend (They went out 4 years), and he told me he did, at the Capitol building. I was a little jealous. This was a month ago. Throughout our relationship, we have always broken up on and off but never stayed apart for over three days. Today, I asked him if I could write my name on his wall, he said "we break up all the time" implying no. He also said that it was an imature thing to do and that he is out of that phase. I was wondering if this shows that he doesnt see a future with me or am I really just being immature.