He is very very confused Geordie. I think that guilt is probably holding him back from making a choice. Hang in there.
Listen to him as a lover/friend. Be the one he can open up to, it will make it easier for him to decide to come home to you. If he is discussing these feeling with her she could quite possibly be angry and scream at him to stay with her, which will only push him away. Make sure you are the "safe" person to come to.
