Depressed I have dental caries... Please help guys.?

Hey guys. I went to the dentist last week after a year (stupid, I know.) needless to say I'll be back to a twice a year schedule again. Anyways, I had a little cavity which he said was caused be grinding or clinching my teeth (I suffer from bad anxiety & stress) which he fixed with a facial filling. I was looking in the mirror yesterday & Noticed on 2 teeth on the bottom, and 2 teeth on the top I have what I think is dental caries (brown spots in the crevices or 'fissures' of the tooth. I used to have beautiful teeth, a little stained from smoking but still very nice teeth. Now that I saw these I was googling images & I think my mouth is rotting. I used to drink a TON of Coca-Cola, and I'd brush my teeth maybe twice a month during this year period (go ahead & judge, but I'm going through severe depression & family matters and It's hard getting out of bed let alone caring about my personal hygiene). I'm just worried that these spots are going to keep growing & growing even though I am becoming religious on my oral health now & in the future. I've hung around with people with rotten teeth & it's repulsive.. I do not want that broken smile. Also, can sharing a cigarette with someone with tooth decay cause it to be infectious? Thanks guys. If I was in any real danger, wouldn't my dentist say "Dave, it's time you start brushing & flossing better because it's getting bad? I mean right now my teeth look good, but these spots have me a nervous wreck & I can't stop thinking that my teeth are rotting as we speak. Thanks & bless you.