I've tried googling composite Juno as well and can't find anything I would assume composite Juno conjunct your Natal NN would be a very good thing, and that if marriage did blossom you would benefit from it, and it would suggest that your heading in the right directionin life. With composite Juno in 9th and conjunct your partners mercury that it could indicate a 2nd marriage (though I don't know for sure). But with it conjunct his mercury and being in the house of higher education...its no Suprise to me that he loves to talk. It might indicate a romance meeting of the minds or one centered on communication and philosophy.
Did you look at your progressive composite? That might tell you more.
My partner and I have composite Juno conjunct DC exactly. I can't remember if this was in the original or progressive. But I'd like to hear more about composite Juno/astroids. It's not easy info to find :/