Advice pls

So this is my first post to Reddit ever. I'd like some advice on bringing that spark back to my bedroom in my relationship. We've been together for 3 years now. We do everything a normal relationship does, we have two houses together go on holidays together at least twice a year but we also give each other our space. Since leaving the army 1.5 years ago I've noticed our sex life has diminished. I'm smitten by my partner and couldn't imagine life without him. We are very open to each other we both know each others passwords to everything so there is never anything surprising. I just wonder if we've gotten too comfortable with each other and I just feel like we need to bring that spark back. Thank you!