There's a guy whose girlfriend is dead and he was super depressed and started sending messages to himself and recovered? I think his mother was worried but accepted it because he started leaving the house again and going to work?? Not sure.

This sounds exactly like the backstory for the 2nd MC (Gotou Hidenori) in Samurai Flamenco, but that's an anime.

It does have a companion manga, Samurai Flamenco - Another Days, so maybe you mean that.

that was it!!! thanks so much