Unfortunately, your tree is declining and can not be saved. Evergreens can hide stress for a long time. (Think of a Christmas tree that is literally severed from its roots for months before it browns out.)

White pines are susceptible to a number of different problems that can contribute to decline. We cannot say for sure what is going on. When pines are stressed due to any type of root issue like poor drainage, drought, poor planting techniques, poor site conditions, they can be susceptible to disease and insect issues. Here is more information on why trees decline due to these types of problems.  https://extension.umd.edu/resource/what-causes-trees-die

Many woody plants have suffered root loss due to the abnormal rainfall we had the last several years. This reduces oxygen in the soil and the roots dieback. White pines will not tolerate poorly drained sites. Then we had a drought last summer and this affects the roots too. When pines are planted closely together they are also competing for moisture and nutrients from the other tree roots. The pine will continue to decline and you will have to consider removal. 

All you can do for your other pines is to make sure the soil drains well. Pines have a shallow root system and will require supplemental irrigation during a drought.

Marian