IS IT MY FAULT DAT MY BF CANT HAVE WIT ME OR IS IT HIM?

OK ME AND MY BOYFRIEND HAVE BN DATING FOR 6 MONTHS AND WE'VE TIRED COUPLE OF TIMES TO HAVE . I GET HIM ALL HARD AND EVERYTHING BUT WEN HES ABOUT TO GO IN ME HE GETS ALL SOFT AGAIN. SO IDK WAT TO DO IF ITS ME OR HIM...HELP!!!