There are several reasons it may have skipped flowering and fruiting. You are right that it needs a couple of years to get established and fruit. Also, bittersweet needs full sun and regular moisture. Great foliage and no flowers and fruit with a bittersweet is a sign of too much nitrogen. Avoid fertilizing bittersweet. Pruning at the wrong time will impact flowers and fruit. Prune in late winter or early spring. Make some adjustments to the care you are giving your bittersweet and it should provide you will berries next year.
Thanks for writing!