Being in love and loving someone.

There are 2 ways of feeling when you are in a relationship, in a nut shell. You are either in love or your not. What is the difference and what makes it change? Some people that have been together for years say that they love their partner but they are no longer in love with them. And many times that's the reason for their divorce. To me, being in love is a wonderful feeling but it can be scary too. You get butterflies (well I still do), your every thought is of that person, and you can’t imagine your life without them. I guess that last part is probably what keeps many older couples together too. You get use to someone, like an old shoe, and you can’t imagine living without them. You see it alot in the medical field. One spouse dies and the one that is left doesnt last much longer. I use to work with a girl I envied. She has been married over 25 years and her husband called her multiple times during the day to tell her he loved her. He sent her flowers, brought her lunch, and always told you (the person answering the phone for her) how lucky he was to have her. Wow…you really don’t see that very often. As a matter of fact, I never have but I always thought it was wonderful the way they treated each other. How do you get that type of foundation and keep it up for that long? What’s the secret? I asked her but she could never give me an answer. It just was what it was. They say you should marry someone you like because the sex appeal will eventually fade. Ya, I believe that. Can you be in love with someone without the sex? Yes, I'm sure you can but if the sex goes away, so does the intimacy and that’s a big part of showing each other how you feel. I'm not saying that a relationship is based on sex alone but its pretty important to me. Of course, I'm 41. I may feel different when Im 70. I want to be in love forever without anything going stale. I have seen proof that it CAN happen. Any veterans of marriage out there that still hold a fire after multiple years of matrimony? Please, tell us your secret!!