I can certainly see why it's a tricky situation - but don't worry... it can get better.
Some anecdotal advice first, in the hope that it helps.
I experienced a similar problem in my V. In the early days, my girlfriend and her husband had hoped that I would find him attractive for at least casual play. I'm primarily into women and do not feel attracted to him at all. In fact, the way he dealt with his attraction towards me killed off any "well, I'm not attracted, but I could do it for the fun of it" ideas.
The way my GF's husband dealt with his attraction towards me was to become very pushy, very pervy, very sulky, very bitter and jealous. If my girlfriend and I were flirtatious or affectionate in front of him, we would throw a tantrum.
It's taken a year and now things are far easier. He no longer pushes for anything from me and says that he is genuinely at peace. He no longer has a tantrum if he sees something between my girlfriend and myself.
How could he have dealt with it better? He could have come to me, calmly and privately, and said that he had feelings for me; that he needed a bit of distance to act appropriately and put the feelings in the right box. I would have been flattered, but more comfortable. How could we have dealt better? We could have respected his need for space and been less demonstrative in front of him.
Whether Danny chooses to tell Michael or not, it might be a good idea to express that he needs a little space. That nobody needs to freak out, but that he just needs a little time. If Michael really is good and pure, he will likely be flattered if Danny tells him how he feels.
In the meantime, if I were in your shoes, I would be careful about how I display my relationship with Michael in front of Danny. I'd be sensitive and try not to rub anything in his face.
6 weeks isn't a long time - I think it will take longer. The important thing is to stay sensitive, be patient, be considerate and be supportive. Ask what Danny needs from you. Encourage Danny to express himself and conduct himself in a mature way, regarding his feelings about Michael.
Do you think that will be possible?
me: female, 29
GF: my primary girlfriend, 39
3 year, open poly V, long distance