my boyfriend gets horny with

My boyfriend gets horny with a picture s of another girl. I saw tons of pictures of a sexy girl in his Deleted photos (folder), same exact girl we both knew and asked him if he gets horny seeing those pictures and he answered yes. I felt insecure and asked myself if I am not enough. ? Is it okay? My trust is fading. We almost spent our 2 years relationship in a long distance type of relationship We already have a 5 Months old son.