My New(ish) Relationship

In September of 2015, my boyfriend and I started dating, we became "official" in October of 2015. I moved in with him fairly quickly after we started dating. Same goes with having sex. It all happened very fast. I am 20 years old and my bf is 29. He is the oldest man that I have been with, only man that I've had sex with. 
Through out the duration of our relationship, things between us are like night and day; Meaning we fight CONSTANTLY. Even though he's almost 30, he acts like a child and it drives me nuts. I try understand where he is coming from but we never see eye to eye anymore. 
In the beginning of our relationship I was his everything. He showered me in gifts and lovey dovey affection. That is nearly all gone now. And I have to initiate sex and other things. 
Ladies, help me out. 💕