I think step one is to change your mindset a bit. You have to understand that your partner is allowed to find other people attractive. If you accept that and understand that it normal, it’ll be easier to start gaining confidence. Just because he finds someone attractive, does not mean he finds you any less attractive. I mean, he’s with you after all, right? Maybe you also need to do things to help you feel more confident, whether that be makeup, skin care, a new hairstyle, new clothes, a hobby, etc. Also, regarding his ex, the fact that he blocked her and didn’t give her much attention shows that you need to trust him more. He shouldn’t have to reassure you every day that he is with you and only you. Working on trust is essential for a healthy relationship, is there any reason you can’t trust him?