People have already made good points here, but I will add my humble thoughts.
1. There are countless reports of finasteride causing erectile dysfunction. People have different bodies and react differently to drugs. Here is one man describing his trouble with finasteride and how the natural treatment Zix has saved his hair instead:
https://www.hairlosstalk.com/intera...ce-how-b6-and-zinc-have-saved-my-hair.101629/
2. It is no secret that pornography and masturbation can cause erectile dysfunction. There are various reasons for this. You can easily find information online. Masturbation exhausts the penis, especially if done often or for long sessions. It adapts to this rough treatment and becomes dependent on it. The penis is an athlete that only performs well if it gets sufficient rest.
When you watch the poison pornography, your mind adapts to it and becomes overstimulated, needing more and more stimulation. It drives your mind away from your woman and true love and passion. Like masturbation, the penis adapts and becomes dependent on it, at least if watched often. Try to fantasize about her instead of your screen.
3. You mentioned that you are stressed and busy and sleep little. These factors certainly can contribute to erectile dysfunction. Low energy decreases vitality, libido, physical strength, mental capacity and more.
4. For some people, taking a zinc supplement does wonders, but if you wish to try it, be careful and keep in mind that it can cause copper deficiency, which can also cause trouble like low libido and energy. A copper supplement can solve this. There are other supplements to try too, such as the ashwagandha that someone mentioned before me, but I would work on the root cause of your problem first.
5. You mention that you have been single for a long time. This can be another contributor because you are not used to the new situation yet. Being nervous makes it even worse. This problem passes with time.
6. There are indeed some tricks around your problem, such as the drugs mentioned. However, something interesting that is underestimated and has not been mentioned here is a penis ring, typically called "c-o-c-k ring." It is cheap and helps attaining and maintaining an erection because it traps blood in the penis. This can be tested at home. Just be careful not to keep it on for many hours. If a woman asks us what the ring is for, we can simply reply that it gives the penis an extra boost. Many men use it even if they have no trouble with their erection. It is common among strippers, for example.
Good luck!