What about him insisting to Piccolo that they shouldn't advance and face mecha Freeza and his father, that their chi are too powerful, whereas before he was brave enough to choose saving Goku both from the RRA brigade and in his fight against Piccolo Daimao, knowing both times how massively outclassed he was?
Besides, it seems that in the RRA arc, when Goku wanted to get his radar fixed at Bulma's house, Bulma was too jealous just at the fact of Yamcha being attractive to the girls, with 0 information of Yamcha reciprocating such feelings he awakened in those girls and that being enough for Bulma to want to pick another boyfriend... it doesn't seem too likely that Yamcha's infidelity would be the cause of their break up.
Yamcha had also a more fine tune of seriousness to his character too, I feel, in DB's first arcs, while later on he basically jobbed at every enemy and isn't given a proper respect moment no longer, even suggesting silly things such as using the DBs to get a necklace for his girlfriend and openly admitting he was the most useless one... I don't know, I feel he wasn't kind of so in-tune with his early characterization.