I would suggest taking a hard look at the elements of your social support network, and trying to determine which would sever their links with you if they knew you were not a Christian.

I do not agree that you are compelled not to lie to people. Truth is a valuable thing, and shouldn't be wasted on those unworthy of it.

Consider that Carl Sagan's protagonist in "Contact", Ellie Arroway, claimed to be a Christian, despite being an atheist. Look carefully at the arguments she offered regarding that claim, and see if they can be adapted to your life.

I would recommend that you refuse to claim beliefs that you do not hold, or participate in actions that suggest you believe those things. Reciting the Creed if you do not accept it is out. Taking Communion if you reject the beliefs that form the basis of fellowship in your church is out. So on and so forth. Don't go to confession if you don't believe you need to confess. Etc. etc.