Actually re-reading the posts I don't know if you should take it for granted that Mono doesn't understand you. What he's worried about is hurting you if he loses his intimate connection with you as a result of your polyamory (right?).
To me that comes down to commitment. He calls you Lilo (lifelove) and seems committed to maintaining his love for you for a lifetime. You both worry that it might not remain sexual (right). Surely if the sexuality goes for one and not the other that is something that in a committed relationship can be worked through?
These kinds of things are a positive for me in polymono relationships because they force us to push through comfort zones that may never otherwise be challenged. "Love hurts". kids get hurt when they go to school or play sport but we would never suggest that we keep them locked up to prevent it.
I agree with the others, enjoy the wonderful present you've created for yourselves and have faith that the future "yous" will be eminently capable of handling whatever comes up. So you may hurt each other a bit in the process. Allowing hurt and loving each other through it is just part of the process.