Hi Assaf,
A good son who keeps in contact with his parents and has a warm relationship with them remains a good son whether or not he is off the derech.
Your honesty and desire to come clean show you are a person of principle, if you stay in regular contact with your parents and have kept quiet about your degree of observance that shows delicacy and hesitation which is natural. I am a mother of grown up boys, and believe me no one can tell or make sure their kids do all they want them to do, it is not right or proper for them to do so. If you have a good relationship with your parents and love them, be gentle and respectful but honest too. Not easy at all, but believe me a polite caring son who is not obsrvant is easier to come to terms with and more likely to be heard and appreciated. Initially they may be hurt and surprised, they may have some concerns they have not aired before but suspected nonetheless. You are their son, and if things are handled calmly and respectfully, then the relationship in the long term will not usually be lost. Your story is far from unusual, your dilemmas have been shared by many, I have been through this with one of my sons, yes I was upset he was not shomer mitzvot but most of all I cared that he knew we loved him and valued him, not just his observance. Things that alter parents perception of OTD children is when a relationship with a non Jew develops as that is crossing a line many of us find too painful to deal with, that is not lack of obsrvance but in my book desertion. To choose a secular life is your right, so is being a good respectful son, give it your best shot, knowing you did your best and showed your parents you still love them deeply is really important. Many young men and women wrestle with mitzvot, as a religiousJewish mother I appreciate honesty above all else. I would hate my son to go through the motions, or live a lie for parental acceptance.