Treat each date like a first date.

I know once you get to be a couple your dating seems to change. If you living in the same house it seems a little weird to be getting ready for a date, while your partner is doing the same thing. To make this seem a little more exciting do this next time you are going to go out. One of you gets ready firsts, then you set a time for your date. The partner that is ready then leaves, to return at the set time. Then the other partner begins getting ready for the date. The partner that is ready can do anything they want until time to pick up their date. You could go hang out at your local pub, or go shopping anything to pass the time until your date. Then when the time come you proceed to go pick up your date. It might seem a little weird to go to the house in which you live to pick up the person you are already sleeping with. Make light of the situation and remember the first time you picked them up for a date. See if you can get those butterflies in your stomach again. Maybe purchase something new to wear that your partner has never seen you in as of yet. It is little things like this that can keep your relationship in the best shape, don't be afraid to be silly and show your partner how much they mean to you.