Priests are human and capable of falling away even more strikingly than just regular laypeople. To fall away as a priest usually involves a pretty big rejection since they are more intimately involved by their lives in the Church. A Catholic can fall away pretty easy by not going to Church then doing other things, a priest has to reject his previous life a little more to do so.
This is not uncommon as the priesthood is not for everyone and the culture of the last 30 or so years has helped a lot. Where is there any support for a chaste life anymore in this culture? Where is there support for a life not influenced by materialism?
We need to pray for our priests and their dedication to service of God. Scott Hahn told a great story about a fallen away priest who came back to the Church, if I can find a transcript of it I will try and post it.
In Christ
Scylla