SHOULD I BELIEVE HIM OR SHOULD I TAKE MATTERS TO MY OWN HANDS?

ME AND MY HUSBAND ARE HIGH SCHOOL SWEETHEARTS. GOT TOGETHER AT 15. GOT MARRIED IN DEC15,2006 WE ARE 18. WE HAD SOME ISSUES SO WE SPLIT IN 2007. WELL HE LEFT.. WE HAD 2 KIDS AND I WAS PREGNANT WITH OUR 3RD. WELL HE WOULD TAKE THE KIDS ON THE DAYS HE WAS OFF TO SPEND TIME WITH THEM.. SO I HAD DROPPED THEM OFF AT HIS MOMS HOUSE WERE HE WAS STAYING.. HE WAS TRYING TO HUG UP ON ME WHEN I HAPPENED TO LOOK ON HIS NECK AND SAW A HICKEY.. I WAS DEVASTATED! I MEAN WE WERE SUPPOSE TO BE MARRIED AND I STILL LOVED HIM SOOO MUCH! WELL WE ONLY SPLIT ONLY FOR 5 WKS WHICH SEEMED AS FOREVER! SO TILL THIS DAY HE STILL SAYS THAT THE GIRL HE MET AT A CLUB JUST DANCED WITH HIM AN GAVE HIM THAT HICKEY..AND THAT HE DIDN'T SLEEP WITH HER. WELL SHOULD I BELIEVE HIM OR TAKE MATTERS INTO MY OWN HANDS AND LOOK FOR THAT GIRL AND ASK HER MYSELF?