That is where trust develops. If you have a real big trauma in your past like a sexual assault and it has an impact on your life today, then if the relationship is to get serious you might want to share that with the person. Just don't share that too early. If you have not come to terms with it, you might want to see a therapist to help put it to rest. Love is a lot more than just having sex every night.
Most couples start to slow down a bit when they have been married for years.
That doesn't mean that you love your partner any less though. When you start entering kids in the picture then things might slow down. In learning the game of love, many times we end up hurting our partner. Sometimes it is intentional and sometimes it is just through ignorance. Sometimes we can recover from this and sometimes we can't.