I'm confused about Chip taking the fall for Tilly & prison time

I mean I get it but in a lot of ways it just doesn't make sense to me. Why would he keep this going for so long? I mean I'm sure he feels guilty too because he was also probably loaded and they both got in the car even though she was driving. I guess I understand that she was an up and coming a lister and she'd probably have been written off professionally in a way in which he wouldn't have been. But still, I'm not sure why Chip would do it.
Is it a metaphor for the complexities of alcoholism? I'm just not sure how to understand his motivations here. Especially to Dennis. I mean he could have a facade with others but why with someone so close to him? Why carry this burden around?

It definitely makes more sense when Chip said to London, "I'm giving you an out" knowing that Tilly actually did it.

Also, I'm wondering about prison time and if he served any.