I'm not really sure what you mean "on the outside".
I survived colon cancer going through chemo with a colostomy bag for 9 months before my colon got reattached. By the time I knew I had it, I was in the emergency hospital and was told if I had not come in, my colon would have ruptured which usually means death.
It wasn't even 5 months prior, that I had a mastectomy for cancer in my right breast.
So pretty much after that emergency surgery and finding out I had another cancer and I had to wear colostomy bag, I was freaked out beyond imagination.
So tell your boyfriend it is possible to recover. He will recover.
If I did it with two cancers, he can do it too.
Best of wishes, with love