"tri-unity"? does that make any sense to you? that's literally "three-ones". it's no longer one. it's three.
Also, infidels are disbelievers and that's all that word means. People who aren't Muslim. Nothing too crazy. You see at this point, I could either bring up the crusades, or some other Biblical warfare-related genocides that would propel this discussion to the deep depths of absolutely nowhere... or I could just tell you that pointing fingers doesn't really help anyone in their limited time here on earth. you could spend your whole life believing something and have it all change in just a flash, so I... a practicing Muslim, will let you dwell in your cyclical mindset and wish you the best. <3