Dear  Martha, 

Novices are at a very critical moment in their formation. It is a time to grow in prayer and self-knowledge, to test their call, to acquire the basis of spiritual and human habits that are going to sustain them in their vocation, and to acquire detachment from the things of the world. It is also a time of study and work, and all in all, it is pretty intense and requires their full attention.

That is why novitiate entails stepping back from ones previous life, and even visitation from their families is usually restricted for the duration of the novitiate. For the same reasons, novitiate leaves only limited room for communication with old friends.

There are additional commonsense human and spiritual reasons when those friends are female.  The novices need to learn if they are capable of reorienting their affective life towards celibacy, adjusting to what that means in the way they are going to relate to women from now on. You can't have the same type of friendship or do the same things with female friends when you are focused on the priesthood as you had and did when getting married was still a possibility. A young man thinking of marriage is open to and even seeking for someone to sweep his heart away, while a seminarian has to guard his heart to be faithful to the one he has given himself to.

God bless.