Now a days the banking is getting smarter day by day. You can control your bank account from home by using computer and mobiles. Trust regarding account using is irrelevant. Cause whenever anyone of us is cashing money from account he/she will be notified by sms. And account statement is always there. Distrust in couples always built from behave, movement and actions taken in daily life. If you wanna sleep with someone behind your wife/husband, you can do it secretly and joint account has no significance here.