You're wondering how to keep a Pisces man wanting you. It's completely understandable to any woman who has ever been in love with a man born under this sign. Pisces men are fiercely loyal when they do fall in love and they aren't apt to stray. A woman who is loved by a man like this rarely doubts his sincerity and feels confident in what he tells her. If you are getting closer to a Pisces, you obviously want to do whatever you can to ensure that never changes.
Learning how to keep a Pisces man has a lot to do with understanding what he finds completely irresistible. There were obviously qualities about you that drew him to you initially. Perhaps it was your honesty or the fact that you were just as spontaneous as he is. Don't ever lose those parts of you. He needs you to remain the same woman he found so appealing.
Pisces men truly need to be with someone who recognizes that at times they need their space. One drawback to dating a Pisces man is that you have to be witness to his ever changing moods. There are often times when he'll pull back into his own sullenness and unless you understand how to deal with that correctly you'll risk pushing him even farther away. You just have to give him the time he needs. Pushing him to talk or trying to trick him into spending time with you when he wants to be alone, will only alienate him. The best advice you can follow is to let him be and just focus on your own life and interests until the mood passes.
He never wants to worry about you being faithful to him.
As you've already been, continue to be the best person you can possibly be. Your Pisces man wants and needs that. Being proud of you is very important to him so show him that there's no one else who could ever be a better partner for him. If you can do that, he'll be yours until the end of time.