He needs to work on rebuilding trust with you that has nothing to do with outside relationships. You have to know you can trust what he's telling you with the simple things or you're never going to know for sure in your heart that he's telling you the truth about the more difficult stuff. Some people just find it easier to lie and to tell people what they want to hear. Sounds to me like he needs to untrain himself from doing that.
Don't agree to anything that you're not 100% comfortable with right now. It's just going to lead to a lot of heartache. Start slow with things that you know you are comfortable with and work on talking everything through. Set aside some time every day to talk about how you're feeling and give each other turns, without judgement, to honestly express how you feel. There are going to be good days and bad days but ALL feelings have to be heard and validated. Boundaries are going to change, it's just going to take time and trust. Good luck.
Everything will be ok in the end. If it's not ok it's not the end.