Tips for keeping that flirtatious vibe with long term bf?

Do you feel like the flirting has decreased between you and your lover as time has gone by?  My bf and I have been together for 3 years and 5 months and I feel like college has been getting more tough  and I've been stressing more. But I noticed we don't flirt anymore. I love him so much❤️ but not sure if I should try flirting again and actually not sure how to anymore? Any tips?