The first note can be added to the Lone Wanderer's Pip-Boy at numerous opportunities, when overhearing inhabitants of Rivet City talking about a possible romantic relationship between Diego and Angela Staley. The second note will be added after telling Angela to seduce Diego.
It seems that Angela Staley has a crush on Diego. Because he's a priest, he's been resisting her. I wonder if this is common knowledge in Rivet City?