Dilemma

So me and my SO have been together for almost a year now and he asked me to marry him about 2 months ago. My past has gotten in our relationship more than it should have ( ex called texted me, what I have done in my past bugs him still)
​We decided to tell eachother everything we have done with other people and when I told him my past he got hurt and it still gets to him. He recently said that my past has came up too much and that in order for us to get married I have to prove it to him. I am completely lost in what he wants me to do to prove it. Please help , I need some ideas because I don't know what to do.