Has your partner seen his GP about his ED? There are some health conditions that can lead to ED and they ought to be ruled out before doing anything else. I have been a Viagra user for years, and it works well for me, even if it is sometimes tiresome to have to take it on a stomach that is empty. Viagra is now available over the counter, but as it lowers blood pressure that needs to be checked before using it. If your partner's BP is already low, then Viagra can reduce it to a level whereby that becomes a problem.
Once you get the ED sorted then your partner is going to feel a lot better about himself and that can only lead to more, and better sex. That in turn will make you feel a lot better about your own self. Invest in some good sex toys if you don't have any. You need to have top-quality orgasms on a regular basis and a vibrator is a real help. You can both use it in foreplay; you can use it on your own. You need to take charge of your orgasms.
As to how to change your body confidence, well it is sort of chicken and egg really. You first have to tell yourself that you are still desirable. When you feel more desirable, you behave more desirably, that gets results in how you perceive yourself, and that in turn makes you feel more desirable. It is a kind of circular effect, and probably the exact opposite to the circular feelings that led you to where you now are. You gained some weight, felt fat & frumpy, acted fat & frumpy, got the feedback from feeling fat & frumpy, and that resulted in you feeling more fat & frumpy. Am I right? I am no therapist, but you have to break that cycle. Could you both do with some weight loss? If so, then work as a supportive team. Success in one area leads to gains in others, and you can soon see improvements. Pamper yourself. Pamper yourselves. Cook decent food and make meals at home an enjoyable event. There is no need to go to fancy restaurants to feel good. Make date nights to rekindle your relationship and invest time in each other. If you have pastimes that the other is not involved in, then do them so that when you are together you feel good about how you spend your time.
Visit the site I mention below and complete the questionnaire to find out more about what your partner might like to try. You could very easily surprise each other with what you might want.
old.mojoupgrade.com/
It is free to use, and is cleverly designed to avoid your partner thinking 'you'd like to try x,y, & z - how gross.'
Best wishes.