Jealousy is often defined as a defensive reaction to a perceived threat a relationship. It is a complex emotion and can be the result of one or multiple things such as: fear of loss, low self-esteem, relationship insecurity, previous betrayals, uncertainty, distrust, etc. While it is normal to struggle with the fear of being separated or losing a valued partner or relationship in an open relationship, there are certain things you can do to minimize it.
Don't run away from your feelings thinking they're wrong or you shouldn't be having them. You have to acknowledge and feel them in order to be able to deal with your jealousy in a rational way.
When/if transitioning from monogamy, allow yourself time and space to transition in an incremental way into an ethically non-monogamous -as much time and space as you might need to get comfortable with it. This will help you set a healthy basis for your future relationships.
Decide on your own personal level of details you want to communicate to each other and to other partners, which can be different from one partner to the other -and that's OK.
Jealousy is often rooted in fear; try to reflect on where your feelings of jealousy is stemming from and try to discuss it openly and honestly with your partners. Vocalize your boundaries, listen to each other, and discuss your fears.
While jealousy is not necessarily an essential part of the experience for all ethically non-monogamous folks, a lot of people do experience and struggle with it. Your feelings are normal and valid.
The ultimate tip is always to: find out what works for you. If you think your jealousy might be rooted in the fear of missing out for example, try scheduling other activities while your partner is away on date. This can be your own other dates, quality alone time at homes, meetings with friends or family, going on solo-dates, etc.