I agree with Adriana on one point, you will never be her and you probably can't replace her with an identical style. It's hard to tell if you come naturally to this role or are playing the part to please him.

It's possible that he senses you are doing this to please him and it's not about you as much as it about you trying to be what he wants. I am not suggesting this is the case, but if it is, then probably it's more difficult for him to come to you because he's not entirely sure you approve, that you won't reject him, that you think what he does is "bad."

Instead of focusing on what he wants and how he wants it, spend some time thinking about what you want out of dominating him. What do you want to do to him? What do you want to make him do, etc. etc. Make it about you. Then share these thoughts with him and see how he responds.

I am not a male submissive, but I am a submissive and I can tell you that for me, a top who is play acting to please me and give me what I want is not what I want at all. What I seek is to serve the pleasures and desires of the top. I want it to be more about him than it is about me.

The more extreme things that he feels embarrassed to do with you are the sort of things he's perhaps needing to feel you are demanding of him... which makes it easier for him to do. This is something you might discuss with him before actually trying, to make sure you are on the right path.

These are just a few suggestions, but the truth is there may just be way more to the situation and he may have simply not resolved his relationship with his former Mistress. I wish you luck.