I'm Alan's third wife only in chronological order. None of us are better or more important than the others. Yet people see to have this idea that we have ranks. They often ask things like, "Don't you worry that he loves one of you more than the others?" The answer: No.
Many people see love like water in the desert. You only have so much, and the more people you give it to, the less each person gets (or one gets a lot and the others get little). Try telling that to a parent. I doubt you could find a single parent in the world who would say that when they have another child that they love each child a little less.
Love is not limited. However, time and energy are, and I think that's where people get confused. They equate time and energy with love. Granted, if you love someone, you will make time for them. But that doesn't mean that doesn't mean that Alan loves me any less because he chooses to spends some of his time with other people.
It helps to understand that you are not the only person in your partner's life. Friends, family, kids, work. We all have things that divide up our time. Even in a monogamous relationship, you can't give 100% of your time to one person. So, it's important to think about how much attention you actually need, and to communicate with your partner(s) about that. If I feel like I'm not getting to spend enough time with Alan, all I have to do is talk to him about it and we can work out a solution.
Jealousy, in the sense of wanting something someone else has, happens. But recognizing that we're human, that limits on time and energy are not the same as limits on love, and with good communication, you can work past it.