Based on my experience if you're really want a long wanking on the bed with your partner.
1. Exercise Daily (Push Up, Sit Up, Squats and Jogging/Running) Do it every single day (This is a reference work out for the anime called One Punch Man)
2. Eat Healthy Foods (Vegetable and Fruit) or make a shake from it
3. Consume 8-9 hours sleep daily
It's simple to read but very had to do.
Seriously I tried this for a month and changed my sex life, no need for a Viagra if you can obtain in a natural way. Even if you cummed on the face/pussy/tits of your partner your dingdong still firm for the next round. The eagerness to fuck till he can't move. As far as I remember, my longest record is 40 minutes non stop. Right now, miss those days, fuck it. Single for Years.!