It's tough, and there are really only two ways you can look at it. Foremost, you have to remember that past experiences make you the person you are, your experiences with your ex-boyfriend will undoubtedly affect your current and future relationships, that's just how us humans work. However, these things can change... It just takes time. As your relationship develops with your partner, your passion should itensify.
The second way you can look at this, is from a maturity perspective. We all remember what it was like back in our teenage years, those crushes you develop, the poetry, the passion, the music, the little kisses, the touches, all passion... Also, all infatuation. Infatuation is extremely passionate and gives you extremely heightened feelings. In time, like all good things, this comes to pass as the relationship develops and eventually love settles in. It's quite possible that you've experienced so much, that relationships have taken on a 'logical' role instead of the more 'magical' role of yesteryear. Things must make sense, there's a certain logic to understanding one another, and the things you do together. This can make things seem less passionate, but lead to greater stability. Many men and women end up taking on this perspective of relationships after some deep (and usually not so happy) experiences in the past.
As a side note, remember it's not just your job to be passionate, your partner has to help bring it out of you too. He needs to be affectionate, but not overly affectionate to the point where it turns you away or makes you feel bored.
Hope this helps,
justin
p.S. I wrote this based on my own experience. :)
