The bible says that the marriage bed is undefiled(heb13:4). The only sex God approves of is in marriage, period.
The bible also says to abstain from all appearance of evil(1thess5:22)-You are living together in the same house without being married and tempting each other to sin.
I feel for the both of you, divorce is painful and heartbreaking. My advice would be that the both of you talk to a pastor, one of you moves out, and abstain from sex until marriage.