Assaf, if I’m understanding you correctly, you no longer want to observe mitzvot, but you do want to maintain a close relationship with your parents. I don’t think you’re doing anyone a favor by not telling your parents about having made such an important decision. They are bound to find out eventually and will feel very hurt that you were not open and honest with them. Even if there could be some way that you could withhold the truth forever, you would still create a rift by not telling your parents the truth about your life, and by the the lying (or prevaricating if you prefer) that is bound to occur, etc.
Your parents will definitely be hurt and upset to hear of your choices, but I think you have to tell them. Be respectful, be gentle, try to be sensitive to their feelings, but do tell them the truth. You allude to “issues at home.” I obviously don’t know what those issues are, but if there is friction between your parents, it’s important that you explain that you made this decision on your own. Don’t leave any room for them to blame each other (or possibly your other siblings or relatives) for what happened. Hopefully, you and your parents will find a way to remain close and to continue to love and respect each other.