There are two ways of seeing your problem; one is premature erection which means you ejaculate early owing to performance issues and the other is erectile dysfunction which you think you’re suffering from. I think you’re suffering from PE which btw is not any disease; most guys face this issue at some point in their life. All you need is a little confidence in you and you need to brush your skills up.
1st of all let your wife know why you’re loosing erection early, let her not assume things, let her calmly you got PE and that way she would be able to understand you rather than feeling displeasure. Next task for you is to practise Kegal exercise which help the guy stay longer in bed, say 10-15 minutes even. I shall attach a link in the bottom for Kegal, go through that and practise it without fail.
As for the 2nd step, I suggest you take proper control of your mind and body. Don’t work your mind too much and don’t get too excited when you’re having sex. Your wife will not go any place, so spend time exploring her body. The universal average for a guy to maintain an erection is 4-5 minutes, while 7-10 is considered good and anything above 10 is very good. All it requires is a little practise.
1st of all spend time in foreplay and make sure your wife’s body is worshipped prior to penetration. Engage in oral sex and make sure she has her orgasm. Now coming on to penetrative part, take deep breathes and follow start-stop method to delay your ejaculation. Whenever you feel like ejaculating, disengage from her or talk to her about something by stopping your strokes and continue once the feeling fades away.
Maintaining a proper diet and engaging in some daily exercises and staying away from smoking and alcohol helps you have a better sex life, so don’t get stressed about it.