The number-one thing to remember about relationships is that at any given time, there are three lives in a relationship. There's your life, your partner's life, and then the relationship's life. Both of you can be doing extremely well, while the relationship is suffering. Being aware of this helps to address the importance of keeping love alive.
If you have separated and now want to rekindle the romance with your ex, your task is to whip out the old metaphorical EKG paddles and zap that love back to life. But it will also take work to keep it going once it's not flatline any more.
One problem is how our society treats people. We see sex sold and marketed, we see image raised to the pedestal of being all-important, while nobody talks about what goes into making you somebody worth sharing a life with: character, personality, attitude, disposition, and integrity.
If you truly love someone, then their happiness is at least as important to you as your own. Be sure to ask yourself, "What is my partner getting out of all this?" from time to time. And then be sure that there is always an answer, because the person who becomes too complacent and takes the relationship for granted will be the first to be surprised when it fails.
Once you have that solved, the rest of the strategy for keeping love alive is to pay attention to the relationship. There's all kinds of things you can do there.
Never be too busy for your relationship. Whether it's work, school, hobbies, business, or the kids and home life, our lives in the 21st century are a continuous source of distractions from our personal relationships. One couple I know who have been together for decades has the "7 o'clock rule": Every evening at 7 o'clock, they stop everything, go in their bedroom, shut the door, and lie down together and talk and cuddle. It doesn't matter if it's for an hour or five seconds. Work, school, the dishes, the kids, or the phone can all wait. It doesn't matter what's on TV. It doesn't matter what's on the Internet. They lock the world out for at least a few heartbeats, just to say that they are determined in keeping their love alive.
Another good tip is to go out on dates. Dates, when you've been married for years? Yes, really, go out to dinner and a movie and cuddle in the car on the way home. The point is that again, you've made time just for the two of you. The rest of the world just has to wait.
One more tip in keeping love alive is every day, give your partner a little present. It can be anything from a shoulder rub to making them a treat for lunch to remembering to turn on their favorite movie for them when it comes on satellite. Or buy them something when you go out. It doesn't have to be flowers and candy all the time, the point is that you went a little out of your way to do something thoughtful for your partner.