A ZBW Supervisor reported THAT positions should have decombined when a busy period was about to commence. The workload and complexity exceeded expectations.

Narrative

I was the Operations Supervisor in charge of an area at Boston Center. ZBWXX was combined with ZBWXY. I knew the hour would be busy at BOS. Therefore the sector would be busy. I did not expect it to be as busy as it got. The individual that was going to be working the 'push' was one of the best controllers in the area. So when I evaluated the up coming traffic; I expected the individual would be able to handle it. In addition I did not think it would be as complex. I did not split the sector before the push. The decision to keep the sector-combined sector was not the right decision. The sector ended up getting over loaded. The individual working the radar position should never have been put in that position. I did send in another CPC (Certified Professional Controller) to track. However; it was too late to split at this point. To prevent a re occurrence I am going to be much more proactive in splitting sectors. I will consider the skill level of a Controller; but not give it as much weight; when deciding to split positions.