Respect his privacy and ask him whether you should keep his discernment confidential for the moment.
It would be helpful – both to you and to him – if you were learn more about his vocation. There are many useful resources on this website to learn more about discernment, seminary life, and the priesthood.
Most of all, pray for him! Give thanks to God for his life and ask the Lord to assist him with the grace of clarity and courage in following his vocation.
Please see this section of the website for more details on the years of formation.
If your son will be pursuing or finishing his college as a seminarian, the Diocese helps significantly with college funding, asking simply that a man help with the cost of tuition at a reduced rate. If he already has a college degree, then all but some personal expenses are assumed by the diocese.
It is important to keep in mind that there is a difference between aloneness and loneliness. In the life of a priest, moments of solitude or aloneness are required for prayer, reflection, homily preparation, and rest. Many priests experience aloneness without feeling lonely. Further, in the midst of his ministry, a priest interacts with hundreds of individuals a week, and many life-giving friendships are enjoyed.
Still, no vocation, even marriage, is immune to loneliness. Therefore, a priest must always be vigilant in maintaining healthy relationships with family, friends, brother priests, religious brothers and sisters and parishioners.