17 y/o Seeking Parent Advice

I’m a 17 year old girl and I have very loving and supportive parents. However, i’ve never really felt comfortable talking to them about my relationships or the possibility of me dating at all.

I hated having difficult conversations to them. I never even came out to them, they asked me if I was gay, and I confirmed it.

Anyways, i’ve dated a few girls before but nothing long term and just never told them. But, i’ve been going out with my girlfriend for about 9 months now, dating for about a month. With prom coming up I want to go with her but I don’t know how to tell my family.

They will 100% support me and have asked if I was going with anyone before, even bringing up my girlfriend. But at the time we weren’t official and I didn’t know if we were dating or even going on dates yet (we’re taking things slow).

What do parents think? Is there a way you’d want? Should I just post it on my Instagram and wait for them to see it? Not tell them at all?

I was originally planning on just waiting until they ask again but with prom so soon I don’t know if they will before it. Plus i’ve denied it every other time they’ve asked (because I really wasn’t dating then)

Side note: I have told them in the past that I wouldn’t tell them if I was in a relationship until I was divorced (jokingly) sooooo….