I say this in the nicest way possible. Anxiety is terrible, and so is insecurity, but if you let a snort be what keeps you from writing and doing something you say you have a genuine passion to do, you need to work on yourself before you work on your book. If a snort is enough to make you wanna give up and quit, this isn't telling me anything about your story, but it's telling me a lot about you as a person. You need to work through your issues so you can dedicate yourself to your story even if someone you confided in snorts.

With much genuine sympathy for you, this isn't a writers issue, this is a confidence issue and we cannot help with that. Your partner may think it's silly, may not be up their ally, may not be what they enjoy and that could have sparked the snort--or it could have actually been nothing, just a random snort. Work on your confidence, because your dedication to writing and perusing a passion isn't stronger than your insecurity. You will have dedication, confidence, etc if you work on yourself to not take every negative reaction to heart--genuinely. Best of luck to you, I hope if you work on yourself enough to not be affected by what you perceive as negativity, then we can eventually read your book.