I think a reality of living with an active addict is that you need to protect yourself from STD's, Hep C, or worse.
Not all addicts cheat, some addictions can cause impotence, but sadly, promiscuity and unprotected sex outside the relationship happens often enough to make using caution a necessity to protect your own health.
You are very wise to get checked.
I am sorry for what you are going through and hope you continue to protect yourself or put distance between you.
Hugs