Happy New Year!

I'm here cause I'm feeling a bit sad. I've been dating my girlfriend for the past 6 months. Our relationship is perfect and we truly love each other. She is an amazing human being!
She is very close to her friends and they've organized a while ago, we were not dating at that momemt, this Christmas and New year's eve trip so they can be together, there's no problem in this right? Right!
She texts me every day, however I'm feeling a bit sad cause she posted some photos and a text like "Could this year start in a better way?" and yes, I'm jealous and I was crying cause I feel that I'm not her priority but she is mine...
I know... this may be all about some lack of self-estime and I know she loves me but I can't avoid feeling ****.
Any advice?
Sorry if this sounds stupid but it's really important for me.
Thank you!