What do you do when your boyfriend's ex still wants to be friends with him?

Someone ask me: What do you do when your boyfriend's ex still wants to be friends with him but you are afraid it could develop into more?

Let him be friends with her. Don't let the jealously take over your emotions, let him decide. Because if you tell him what to do, and he doesn't like it he'll find a way to be her friend behind your back if that's what he wants to do. Plus, they broke up for a reason, and he is with you now. Although I'd been burnt once on this, relationships are built on trust, love and respect, so you must love him, otherwise the relationship is pointless. If he loves you and you love him, trust him to make the right decision.