How does tea cake convince janie that his feelings for her are sincere

Although Janie does not trust the sincerity of his feelings, he keeps coming back again and again to flirt with her, to spend time with her, to spend an entire evening with her, and to take their relationship public.  He works, buys a car, and in general tries to prove that their ages are not a hindrance to their intimacy.  He wants all to know that they are an "item."