Dear Mark,

I am not going to get into the theoretical question whether God can take away a vocation or not, because God is God and yet at the same time he does not repent of his gifts. Let me rather address the practical question behind the words you wrote and which we could phrase as follows, would it be right for you to pursue a vocation even if you have had these difficulties? Is there a point in insisting on going ahead with a vocation, would it even be prudent? 

There are several variables that I would not expect you to go into in a message like this but which have a direct bearing on the answer, so let me just mention some of them so that you can go over them with your spiritual director or confessor to find the answer in your own case.  One variable concerns the length of time you have had these problems.  Did these problems arise relatively recently, when you were already engaged in your discernment or have you had them a long time? In the former case it would be important to examine to see if something in particular triggered them, and in the latter it would be important to consider how long you have been trying to overcome them, how you have gone about it, and what progress you have made.   Another variable is the nature of your problems. Do they consist in thought only or also in actions, do they involve use of the internet or other media, is it something you engage in alone or with others?  Another factor to consider is their frequency. Obviously, and ingrained habit is a very different matter from an occasional lapse. 

It also helps to examine if your faults are influenced by other factors, such as use of alcohol or peer-pressure, because sometimes these weaknesses have their root causes in areas that are quite different from the fault itself, and our action in overcoming them will be much more effective if we concentrate on the root fault. Also, it is important to examine what are known as the occasions of sin, not their root but certain avoidable circumstances which do influence greatly my actions (such as the friends I hang out with, or the websites I look up on the internet).
   
It is in reflecting on these points and similar ones that you will be able with the help of your spiritual director (or vocation director) prudently to decide if you should pursue the priesthood.

There is something else in the background of your question, which I think we need to address clearly. You say that you can feel your vocation fading, and hence your question if this might not be God taking it away, implying that he is doing so in punishment of your sins, and that is the end of his plans. The logical consequence of this would be despair, feeling Ive let down God; my life is now useless since I cannot undo the mistakes I have made...

That would be the biggest mistake. It would be a denial of all God is, and a denial of all we are into the bargain for we are not that great that we can do what God wants perfectly, without having to have recourse to his mercy and pardon daily and not only occasionally. We have to live in that realism, and live in the present. We can learn from the past but we should not get stuck there, as if God couldnt bring good out of evil and give us a new mission instead of the old that for some reason, maybe our negligence, went astray. Not only can he, but he wants to. That is the way he works.

If it turns out that your spiritual director tells you to leave aside your thoughts of a vocation your next step should be, Lord, I put the past in your hands. What do you want me to do now? 

I hope these thoughts help you.

God bless,