That's illogical. Saying that "A could do B under certain circumstances" IN NO WAY implies "A could do Z". You're not making any sense. At all.
I could totally see Peter getting less careful when depressed and shocked, and because of the situation (a wedding!) and the fact that he's not used to drinking I could totally see him get drunk. Is it stupid? Yes, getting drunk IS stupid. (which is why I don't drink) Nor is Peter exactly foreign to bad rebounds.