You're very brave!
First off, I applaud you for not running for it right away. I have experienced that from the other side and it sucks. It takes courage to come out as a poly. It is also brave for you to try to make it work.
I admit, it is emotionally scary. Keep an open line of communication. When I have crazy jealous thoughts, I will flat out ask my boyfriend if that's a realistic point of view "...is that what you're thinking?" (usually it's not even close).
One book that really helped me to understand the "why's" of polyamory was Sperm Wars. It's more of a biological explanation. A book called The Ethical Slut helped with the social aspects and also describes different types of open relationships.
Books aside, this is how I see it. In monogamous relationships, it seems one partner usually cheats or wants to cheat. Even though you love somebody you may have crushes/sexual feelings for someone else; that's perfectly normal. An open relationship is a respectful way for everyone to get their needs met. It's a way to explore those feelings (sometimes within parameters) in a way that is not meant to hurt others.
And it's not like it's a sexual free-for-all (although some poly couples are okay with that). Every couple is completely unique. Everybody has their own guidelines/rules to go by. I really recommend that if your friend is willing, you discuss what their rules are and let them know your boundaries as well. Knowing what is and isn't going to happen between partners is a nice way of ensuring that everyone feels safe, secure, and well taken care of.
After reading the Ethical Slut, my boyfriend and I drew up and discussed our own safety rules. For example, one of his rules for me that makes him feel more secure is that I am not allowed to hold hands with the guys I sleep with. That is reserved for us alone. Which by the way is another thing that may make you feel less jealous. Maybe you can have some special act or even affectionate nickname that only you two share.
Also, for dedicated couples, it is really reassuring to have a ritual. When I come home from another guy's house, I make sure to make time for my honey. I hug him and kiss him and let him know I love him. I spend special time with him so he knows he's still important to me.
I think it's important in an open relationship to lay out expectations of each party involved. Really know what motivates each other. Many people think being poly means treating everyone like a meat puppet but to me, a functional poly relationship means juggling everyone's expectations and emotions.
I hope this helps and if you have anything to ask, please do. Keep us updated! We can all learn from each other's experiences.