you have to realize that you will become more comfortable with the situation at hand as time goes on. when a relationship is involved, it's natural for humans to react with jealousy or insecurity when it involves their partner being sexually or emotionally active with other people.
ive known a few polyamorous couples, and while the idea of it is incredible, from what i've seen, it's more incredible in theory. i think you have to have the perfect match for it to work well, and not let it fall to shambles. for instance: i knew a polyamrous couple that was together for 7 years... however, the woman usually engaged in sexual acts with other women, rarely ever men, but in some cases, yes. the man, however, would engage in "relationships" with other women, where he wouldnt be sexual with anyone but that girl and his SO. i couldn't possibly understand how with his SO, they could have a polyamorous relationship, just so that he could have a "monogamous" (in a sense) relationship with other women at the same time. needless to say, after 7 years, they ended with a divorce. <p>
it's definitely an issue of maturity and communcation, and if you both have great skills in each, then good luck to you! it will definitely take a while to get over the insecurity that's going to come along with an open relationship, but perhaps discussing things in details or setting some rules at first will help out.