Your sentence becomes correct if you change "you" to "your". Without that change, the sentence is wrong because the preposition "to" needs an object, and that object needs to be a noun or noun clause. For example, you can say "What happened to chocolate?" or "What happened to Sam?" or "What happened to singing songs?" The third example works because "singing" is a participle behaving as a noun. Likewise, your sentence works with the noun "coming". However, since it is a noun you need to say "your coming", just as you would say "your chocolate" and not "you chocolate".

Not wrong, but simpler is Why didn’t you visit me this weekend (as you’d/we’d planned)?

It sounds a bit awkward that way. Here are some possibilities: Informal and polite: I thought you were going to visit me this weekend. Did something happen? I thought I would see you this weekend. Is everything all right? Informal and direct (therefore less polite): I thought you were going to visit this weekend. What happened? Weren't you going to visit this weekend? What happened? More formal and polite: I'm sorry I missed you this weekend. Is everything all right?