A love with an expiration date isn't love at all.
The feeling of love might lingers on, but the door for the relationship can't be kept open forever. Those two things are usually closely connected to each other, but ultimately they are still different things.
Kind of like gasoline and motorbike, I think. If you have both, you can go pretty smooth and far, as long as you maintain the bike and refuel regularly. With only the gasoline, you can still do something with it, but you can't go very far and it's easy to get burned. With only the bike, you can maneuver and push it along, but you can't go really far, either, and it's tiring and frustrating. And your can even use different types of fuel, but you will have to adjust the bike accordingly to avoid problems.