My boyfriend has serious trust issues, how do I let him know that he has nothing to worry about?

I think you need to sit him down and have a serious talk with him. You need to let him know that honesty and trust are a major factor in your life and your relationships, and you want him to feel the same way. Without it your relationship may suffer in the end. Ask him what you need to do or say to convience him that he is the only one for you. Let him know that you would never have him lose or give up anyone that he thought where good friends to him so that is where your friends stand with you. You would never give him an ultimatium that would cause you or him trust. Goodluck