Where I live a prescription is required. Even if it is not where you are, do you think you should talk to you doctor first? You might just need some long chain omega-3 s in your diet. Try some sardines but ones in water not oil. Avoid seed oils. What is your blood pressure like? If it is too low that can affect your sex life. 10% of the population has naturally low blood pressure.
I agree with the "see your doctor" advice. I started having B/P issues a few years ago and got it under control. The result is my erections come and go now instead of staying the course. Not good as when fucking my cock would go limp while thrusting into her pussy. Talked to my doc and he put me on ED meds. Got the correct formula and dosage nailed down and can hold my erection from start to finish and then some. On line doctoring can't check your body like in person doctoring can. Plus I take the prescription to a pharmacy where I can use Good Rx which cuts the costs.
I have heard of cases high blood pressure preventing an erection, but cannot see it cause a dick to go soft once hard. Unless you have FH then Statins are not a good idea. Remember testosterone is made from cholesterol.
In the UK, you can go to online pharmacies or visit the pharmacist face to face and you need to fill in a form. If it is an online pharmacy you must check whether it is genuine. Depending on your medical history you will be offerred appropriate ED medications. Generally branded products like Viagra or Cialis are more expensive than generic versions like Sildenaphil or Tadalafil. Generic products are equally effective.