Communicate, communicate, communicate Jealousy, envy, and scheduling problems can all be minimized by effective communication. Even the best-intentioned couples have years of dyadic habits to break. You can help them, and yourself, by being clear about your needs.
Know thyself You are entering into territory for which society offers little support. If you know what you're doing and why you're doing it, you'll have a far better chance of succeeding with it.
Be conscious of how you feel about bisexuality If you're not fully comfortable with your bisexuality, you'll feel confronted frequently when you're with your couple. This is a normal feeling during periods of personal growth. But if you can keep all three of you aware of your level of discomfort, you may help avoid awkwardness should you wish to back off, even momentarily.
Be sensitive to the primary/secondary difference Regardless of how much love and heat are present at the beginning of a triadic relationship, you'll be less connected with the people in the couple than they are with each other, just because of the time they've logged together. In the beginning, this can actually be a comfort; there's less at risk if you're not as close. But if the relationship is succeeding, this can become uncomfortable and should be openly discussed. (See point number one!)
Maintain your own boundaries Diving into a couple's life can be so rich and interesting that you lose track of yourself. Remember that their "stuff" is about them, not you. Don't permit yourself to be drawn into their couples issues just because you trigger them.
Do yo love both people in the couple? If you're far more attracted to one of the couple, or, worse, are attracted to one and are tolerating the other, you should consider a polyamorous relationship different than a triad. If you're open and honest with yourself and them, you might be able to have a one-on-one relationship in the context of their committed relationship.
Fasten your seat belt Because you're melding with an existing relationship, you'll be experiencing change in your emotional, mental, and social life far more profound than they will. Cut yourself some slack, and ask them to cut you some slack, if the rate of change becomes too great for you.
Take it slowly Three people won't fall in love, take emotional risks, and alter life plans at the same rate. Respect everyone's discomfort levels with the changes you're going through, and take it no faster than the slowest of the three is comfortable with.