Boyfriend TROUBLE! WHAT DO I SAY AN DO 2 MA BOYFRIEND ABOUT THIS SITUATION?

OK 2 SUMMARIZE IT: HE HAS THIS FRIEND THAT WERE BOTH COOL WITH ONLY THING IS A COUPLE MONTHS BACK SHE TOL ME THAT SHE LIKED HIM IM LIKE WHAT?? SO I TOL HIM 2 STAY AWAY 4RM HER NOT 2 MENTION THE GIRL IS ENAGED 2 BE MARRIED!! WELL ANYAYS A COUPLE DAYS AGO SHE TOLD HIM THAT SHE SAW ME TALKIN WITH SUMONE ELSE THEN WE KISSED! SHE CLLED MA BF AN TOL HIM THIS CUZ WE LIVE IN DIFFEENT STATES BECAUSE OF COLLEGE! HE GETS UPSET AN WAS MAD AT ME BECUZ HE THOUGHT IT WAS TRU AN IT WASNT IM MAD AN HURT BECAUSE IM LIKE IF U LOVE ME LIKE U SAY U DO THEN U WUDNT LET WHAT SOME GIRL WHOL LIKES U AN WANTS 2 BE IN MA PLACE TELL U THAT SHE SAW ME DOIN SUMTIN U KNO I WUD NEVER DO! HOW CAN U SAY U TRUST ME YET U LET HER TELL U SUMTIN THAT CUD HURT OUR RELATIONSHIP? CAN SUMBODY PLZZZZZZZ TELL ME WHAT 2 DO I MEAN WHAT AM I SUPPOSED 2 SAY 2 HIM? 2 HER? HELP ME!!