There wasn't much anyone should have felt poorly for Constantine for. He made his own luck, and didn't keep that fact a secret. Anything he did or did not do when it came to Carol was his own choice.
His choices weren't always good, mind. John was the sort who often fell into the same idiot traps, particularly where human interactions and relationships were concerned, and while he wasn't thinking on it too hard -- or maybe at all -- it wasn't like it was impossible to see that it'd probably happen all over again.
Carol hated waiting. Carol hated talking about feelings. About not being in charge of every choice having to do with herself (and, consequently, others). And John -- he could work with those things. He wasn't a feels-y sort generally (although he had his moments and he'd been with his fair share of people who could attest to that), and preferred to keep things close to the vest. He wasn't worried about being in charge, and he was rarely late. So. That all evened out.
When John showed, it was just about ten minutes later, and it was in his usual manner of seeming unaffected and looking fantastic in a trench coat. He liked being consistent.