Help opinions please

I need some serious help. I need some opinions. My husband and I have been married for 4 years. We have had a far share of ups and downs. I have made a couple big mistakes and my husband has stayed with me threw them mistakes(cheating) and I've had to earn my trust. Well just recently we have been having some major problems and stuff, the other day I got home from picking up my daughter.. I walked in the house and he had pipes, and a mirror on the table with a white powdered substance(meth) he wants me to forgive him and I cant. Should I forgive him since he had forgiven me for many things or should I walk away?? Please help!!!