He may have one of the following kind of erectile dysfunction-
1. Psychogenic/ stress induced... Most common . Ur BF of young and healthy, most probably has this. It could be due to anxiety, lack of arousal by partner, etc.
2. Arterial - insufficient blood supply to Penis.
3 neurogenic - defective nerves carrying signals for erection to penis
A physical consultation with an experienced Urologist is required to identify which of the above he may have and
According to the diagnosis , treatment shall be prescribed.
Next Steps
both of u consult an experienced Urologist