I hate his new girlfriend and I'm sick of seeing her everywhere

Throwaway.

I (35F) had feelings for a man (31M) that was a close friend for several years. It never worked out because we were always dating different people. We started sleeping together at one point when we were both single, it lasted probably 4 months, and I thought we'd get together, but when I pushed it he said he didn't feel the same way and wanted to go back to being friends. I stupidly tried to push it again a couple times when we hung out, but he never went for it. My therapist eventually told me to cut him off so I did. We still follow/like on social media but we haven't spoken or seen each other in over a year.

He posted his new gf over the summer and I googled her up after looking at her profile. The only thing that came up was the website of the school she works at. He never wanted me, but is now with some little petite teacher who looks like she's 10. She's in her mid 20s and he's in his 30s, which is gross to me because maturity levels are different at those ages. All he does is post pics of them, pics of her, places they go, food she cooks for him, he's so proud of her and blah blah blah. It's the only thing I ever see. I'm a fucking lawyer and she spends all day with 5 year olds telling them what colors are.

I hate feeling this way, I want to block him so I never have to see her face again but his account is private and I know I'll want to refollow. I'm with someone now so I shouldn't even be thinking about him, but it's hard not to when I constantly have to see pics of them together. You would think they've been together for YEARS based on the amount of photos posted...nope, 8 months. I blocked her on instagram so there's no chance I'll have to see her face again unless he's posting her. I have no clue if she even knows who I am or if he's told her about our fallout. Part of me wants her to know, part of me doesn't want to even take up space in her mind.

How do you even get over someone you had such strong feelings for going for someone so much lower than them? I wouldn't feel this way if he was dating someone out of his league, but he got with a woman less successful and less pretty than me. That fucking stings. She's going to move across the country for him. I have to find all of this out from mutual friends.

How am I supposed to make sense of him not wanting me but being completely OBSESSED with her? Why is his relationship so humiliating for me? I'm mad at myself because why the hell do I care that he's happy with an average (at best) woman?

tl;dr- Guy I had feelings for got with someone below his league and I can't cope with seeing them together all the time. She's less accomplished than me and I don't understand why I'm not good enough for him but she is. It's driving me insane.