Was I wrong to question him...?

No you were not wrong to question him. That kind of behavior change is a big red flag. People do not just change overnight. I would wonder to what is going on. Is he cheating doing drugs going to the strip club I don't know. But something is causing the change. But to just assume he is cheating you have to be careful there. Maybe someone he works with told him he was a miserable @sshole and that caused the change. Just keep the lines of communication open and maybe you can find out what the reason is.