It can be very exciting when you feel that you've found "the one," but keeping a relationship strong and healthy takes effort. To hold onto your girlfriend long-term, you'll need to understand what girls want in a relationship and what makes long-term unions work out happily. Knowing these tips makes it more likely that the girl of your dreams will want to stay by your side for a long time to come.

Be Her Hero

For long-term relationships, many girls really want a romantic hero, according to 2003 research led by Daniel J. Kruger of the University of Michigan. In a study of heroes from literature, the undergraduate girls surveyed picked romantic, moral, monogamous characters over domineering, promiscuous men for who they would like to settle down with. The study, published in the journal Human Nature, found that the longer girls imagined being with someone, the more likely they were to prefer a mature, stable guy. Show your maturity by studying hard and staying out of trouble.

Don't Get Obsessed

It is possible to keep the fires of love burning in the long-term if you make romantic gestures, researchers at Stony Brook University found. But don't make the mistake of trying to replicate the early stages of the relationship. While intense passion is good in the short term, being too smothering with your girlfriend could very well lead to a lack of relationship satisfaction in the long-term, revealed the 2009 report, which was published in Review of General Psychology. Giving her a foot-rub is romantic; kissing the ground she walks on is over-the-top.

Show Your Warmth

What girls most want in a long-term boyfriend is kindness, warmth and openness, researchers at Illinois State University and California State University revealed in a study published in the Journal of Social and Personal Relationships in 2002. Demonstrate warmth and kindness by cuddling your girlfriend often and letting her unload when she has problems. Show her you're a keeper by being open about how much she means to you, and how special she is.

Appreciate Her

When your girlfriend treats you well, showing your appreciation can make her happier with your relationship in the long-term, research published in the journal Emotion showed. Being shown gratitude by a significant other had long-lasting effects, with the person being appreciated reporting more satisfaction even quite a while after the gratitude was expressed, psychologists at the University of North Carolina, Chapel Hill, revealed. Your girlfriend will feel validated and cared for if you remember to thank her for doing nice things -- from little favors, such as recording your favorite show, to bigger things, such as buying you a gift.