I know I can't change my boyfriend but how do I get him to be more romantic?

Can't change ? How come u can't change him ? If u have more agreement. Than disagreement i understand , if not u may need to think is he really what i want?
Talk. Be open and honest with your boyfriend about your feelings, your thoughts, your fears, your expectations, and ask questions about his expectations. You might be assuming things or expecting him to read your mind. Honesty and communication is a critical part of making a relationship last.