I was once infected with std and i was well treated but now my testes i touch they cold. i want to why? or is there another problem remaining?

Diagnosis: Cannot diagnose this on the internet. You should see a primary care physician and provide a full history and submit to a physical examination.

Scrotum cooler: The scrotum needs to be cooler than core body temperature to preserve the sperm. This is probably what you're seeing. Unrelated to std.

Normal & not related: You are feeling your scrotum which will normally feel cooler unless you are wearing jockey underpants at the time. Incidentally, testicular temperature is supposed 1/2 to 1 degree cooler than temperature in rest of body for optimal sperm production & function. Hence boxer underpants should be preferable to maximise male fertility.