''I, Bertram, take thee, Billy,'' chanted the white-robed clergyman. '''I, Bertram, take thee, Billy,' ''echoed the tall young ridegroom, his eyes gravely tender. ''To my wedded wife.'' '''To my wedded wife.''' The bridegroom's voice shook a little. ''To have and to hold from this day forward.'' ''To have and to hold from this day forward.'' Now the young voice rang with triumph. It had grown strong and steady. ''For better for worse.'' ''For better for worse.'' ''For richer for poorer,'' droned the clergyman, with the weariness of uncounted repetitions.