It is possible to have low libido or ED. This can be caused by different things- low testosterone levels, prostate problems, diabetes. He may want to rule out the medical causes first. Then, he can explore if any emotional triggers are causing this. There are different options besides Viagra- Macuna pririens and Tribulus are quite commonly used. Hypnotherapy can also help with this.
If you believe that this is a couple's issue that working with a counselor such as a sex therapist, then you ask him if he wants you to participate in his treatment.