Last weekend we watched the movie "Vicky Cristina Barcelona" with a friend. It's a good movie, what you would expect from Woody Allen. It's about the love, passion, marriage, relationship. There was part of the movie that a middle age wife who was cheating on her husband was confessing 'she loves her husband but she is not in-love with him'. The idea of the movie was to show a life of good couples who are each normal people but there is not enough passion between them.
From wikipedia : Passion is an intense emotion compelling feeling, enthusiasm, or desire for something.
If you ask me passion can be a strong motivation for two persons to start serious relationship but it's not enough to build up long-term relationship and it's definitely no guarantee that the relationship will work. When two persons attract to each other at the beginning everything sounds very passionate. But as time passes when they know each other much better the passion replaced with real love if the two matched. Everyone might have his/her own definition of love. For me true love is not based on temporary passions comes and goes like a wave, it's a deep feeling you have for someone based on real knowledge of each other. It's a feeling you have for someone you can't live without.
Some people are a loner, they love to be free and live without the idea of committing to a single person. They keep the relationship as far as the passion is high and when it goes down the relationship is dead for them. But for those who are looking for long-term relationship, passion is just one of the required ingredients to build up healthy relationship. You might attracts to someone but also you couldn't stand staying with him/her under one roof for more than a week. Attraction/chemistry is something you need to initiate the relationship but for a life-time relationship you need something deeper than initial and temporary passions. You need to really love your partner the way he/she is, not the way you are imagining him/her.
What I want to say is that don't mix passions with love, you can love somebody deeply but your heart beat doesn't rise up or your cheeks blush every single day you see your partner. It dose not mean you guys have problem or that's the end of the relationship. Visa verse it could means you guys pass the initial phase of the relationship and now with your feet on the ground you have something deeper and more meaningful.