If you dream of being unfaithful in love, you will be entangled in a situation that is not in your best interest, perhaps even illegal. You may have behaved in a way that compromised your values.
To dream that you are being unfaithful with your boyfriend’s friend means you are feeling neglected by your boyfriend.
To dream that your sweetie is cheating on you, means you are scared of being abandoned. You may feel some lack of attention in the relationship.