You must try to stand back from a relationship and view it as objectively as possible. You tend to create an idealised vision of the affair, which you confuse with the reality.
Thus you must take care to be completely honest and straightforward with your lover. This may require a lot of unromantic, down-to-earth discussions, which are likely to seem trying, but in the long run the rewards will outweigh the bother.
This kind of carefulness will help to defuse the jealousy that often arises with this aspect.
Not only is it important to make your positions clear, you must then abide by them and not back down or fudge on your promises. Trust is the most important pillar of a love relationship, no matter how unusual the arrangement is.