Could it just be me ?

My bf and I have been together for about 10 months , and we've fuss about communication problems and so much more. I tell him that he is guarded and don't want to express his feelings and he blames everything on his past . He doesn't want to tell me what happened and what made him so mad I feel like he's trying to not make the girl look so bad . I mean I wouldn't judge anyway but I still think he thinks about her