wondering if it is a time requirement to consider an A an LTA or is it an intensity thing
It is considered a LTA based on the length of the affair. It's never been completely clear to me about how long before an affair is considered a LTA. My FWW's affair was 3 years and I consider it a LTA. However, I know there are SI members that had to deal with affairs that went on for decades.
Whatever the length of time/intensity you are dealing with, if you feel you would be better served by calling your WS's affair a LTA, then I don't think anyone would object. There is a LTA thread in the I Can Relate forum you may find helpful. Perhaps you can read some of the posts there and see if they relate to your situation.