You say that you and your partner use manual and oral stimulation, since you’re no longer able to have intercourse. Your partner requires extended stimulation, and you’re wondering what might help.
Stronvivo is a nutritional supplement developed for men’s cardiovascular health; it’s been found to significantly improve sexual health--because circulation is integral to arousal and orgasm. It is used for both male and female sexual health, improving both desire and function (ability to arouse and orgasm). I’ve had many women report improved ability to orgasm, and the clinical trials report the same for men.
The other factor to consider is medications that may be interfering with orgasm, or hormonal factors, like low testosterone. I’d strongly recommend a conversation with his physician, if he hasn’t already had one, to see whether there are health factors to consider.