Communion is a powerful ceremony that has been stolen from the church. Communion is a remembrance, it's not something you should avoid if you sinned this week. If we could only take communion when we're sinless, we'd never take communion.
Think about it, "anything not of faith is sin." If that's the standard, then you'd never take communion. Communion is a ceremony to put you back in faith toward God and what he's accomplished through Christ. It's a meditative exercise where you engage your heart with the fact that you died with Christ and you're washed clean in his sacrificial blood. The life is in the blood, an exchange happened, you should celebrate that!