trust

Me and my boyfriend have been together for 3 years in the three years we've been together he made a mistake and kissed someone as a mutual friend in our first couple months of dating and i forgived him for it and we've moved on

now i know with relationships there is suppose to be trust but sometimes i don't know how to trust him . Some days i do. OTHER DAYS i don't.

Anybody has any advice on giving people trust again . Because i love him and i do want to trust him again and not drive him away