Not from experience of ED, but there is the refractory period. Traditionally, this is defined as the period between cumming and being able to get erect again but, as it is caused by hormones released into the blood at the time of orgasm, and as hormones are gradually removed (usually by the liver/kidneys) the end the of this refractory period isn't going to be sudden in the sense that one second no amount of stimulation will have any effect and the next second the slightest touch will make you rock hard.
What I would expect is that in the minutes or hours after your last cum, the longer it's been the easier you will find it to get and stay erect. Given that it is possible to masturbate without being fully erect it would be possible to masturbate so often that you never fully finish your refractory period, i.e. where you get erect naturally.
Could that be what is happening for you?
So, sorry I'm not sure I understand everything (I'm French), but I'll try to answer.
- Yes, I often masturbate without really being erect.
- Sometimes I'm erect for the first few minutes, but after a while, I become less hard.
- As I said, most of the time, I put a lot of time to ejaculate, since years. I remember, that the first years, I held back, I slowed down to last a very long time. But now, I can't ejaculate, it doesn't come for an hour or two or more. And even when I ejaculate, I sometimes have a feeling of frustration, like it's not complete.
- I have a bad habit of using cockrings to try to maintain my erection, it is as if I could no longer have a very hard and long erection withou
- I watch a lot of porn, pretty much throughout the day in small amounts, and in the evening in larger amounts. When I watch porn during the day, I masturbate a bit in my pants, without really being erect, and without going as far as ejaculation.
- When I masturbate I have to do it energetically, even if I use a fleshlight I have to go like crazy. I don't know if I am clear.
This situation is quite difficult to live with. I already have a lot of problem with sex, but I think it's the most humiliating. I would really like to find a solution.