Discovering my (burning) jealousy

Hello! First of all, thank you for your answers which are always so enlightening and interesting.
I have a question about jealousy.
I have been with my boyfriend for 8 years and we are an exclusive couple and we trust each other. We’re not the type to act jealous, ask a thousand questions or stop the other from going out. I’ve always thought that it’s important not to lock someone up, not to smother them, if you want the relationship to last, and that trust is there. I’ve never acted like a jealous woman and never felt the need to do so.
However, in the last few months, I have found myself extremely jealous and I am in a lot of pain. My boyfriend is a photographer and shoots beauty models (and this is new). He posts them on his Instagram account with captions saying how beautiful and nice and wonderful these girls are etc etc, and it hurts me like hell and I don’t understand why. The fact that our couple is currently in crisis (he loves me but is a little lost emotionally at the moment he says, I feel like a middle life crisis) does not help me to stay serene.
All I do is look at these photos, the captions, a thousand times a day, and think how old, ugly, uninteresting I am compared to these girls. And I feel humiliated that he writes these things publicly about them. I don’t know what to do with these negative feelings of jealousy and self depreciation and anger, which make me suffer and which I’m not used to (I need to specify that my boyfriend says he loves me and that I’m beautiful, I’m lucky for that).
Sorry, my message is long and rambling! And I don’t have a very clear question… Would you have an advice to give me ? Can you help?
Sorry again!
Thanks a lot!