I imagine Deku to be the type of son that likes to share happy stories and memories to his mother… so naturally if he gets into a relationship, his mom will know all about it.
Exception to the rule of sharing happy stories would be, of course, anything related to One for All. But I think aside from that, Deku would share most positive things that happen to him. (Only positive things, because Deku wouldn’t like to make his mom worry.)
Cheloneuniverse 