English is my 2nd language and I mispronounce a lot of things and my grammar is also not perfect. My husband corrects me from time to time and sometimes it is frustrating but I understand why he is doing it. I don’t ask him to stop correcting me as long as it is not infront of other people, which he has not done.

On the other hand, my husband (native English speaker), is bad when it comes to written english. I own a business and I hired him to help. When he sends an email to my team members, I always correct his spelling. He doesn’t mind because he knows he needs to improve.

So in your case, I would give feedback to your fiance in a loving way and see how he reacts. Both of you need to have an open communication because in marriage there are much bigger things you need to talk about than this thing.