How do i deal with my husband is constantly thinking i'm cheating on him?

Challenging: This is challenging. Sometimes this situation can result when there's been past infidelity, and trust has not yet been restored. Also it can happen when one partner projects his/her own issues, and becomes suspicious of the other as a result. Or it can be part of a psychiatric illness such as delusional disorder or paranoid personality d/o, etc. Couples' counseling may be a start for you both.

Family Therapy: By seeking family therapy , u can explore why he is thinking that and perhaps making him change his perception, however, if he is paranoid and or delusional than he may need additional medication. My advise to act asap and try to see a therapist...!

Safety first: A word from a police pathologist. I'm sorry about your situation. In a perfect world, everyone would be willing to get and learn from good counseling. As dr pappas points out, your husband may have a grave mental health issue and your physical safety is most important. If he does something to make you feel you are in physical danger, get out and stay out before there is any further confrontation.