Separation Anxiety Setback

I have a Jack Russel Dachsund mix, hes about 7 months old now and I got him when he was 3 months. Hes been a velcro dog since day one, like he will get up and follow me to the kitchen even if he was sleeping. I work from home so Im with him a lot and he sleeps in the bed with me. Long story short I have been working gradually on leaving him alone and got up to a few hours at a time but had a major setback recently. I went to the movies and got back 3 hours later like I have many times and nothing unusual. But the next time I tried to leave him alone he just started trembling in fear like Ive never seen before.

Here's what Ive done so far:

I tried crate training after he was comfortable in the house at about 14 weeks and the first time he freaked out and tried to bite his way out of the crate, his face got stuck in it and he started screaming, one of his puppy teeth ripped out and he was bleeding and scared. So pretty much immediately I gave up on the crate and started making the bathroom puppy proof and decided I would leave him in there instead. Started small with a minute, few minutes, 10, 20, etc. I got to the point where I could leave for an hour and then more, all over the past 4 months. I would stay for a couple minutes talking to him and giving him treats so it didnt surprise him when I left. I pretended to leave and monitor him and after about 10 minutes he would quiet down and he would be quiet when I got back so I figured he was settling okay. Coming back it would always be a mess, he spills his water and food, chews his potty pad, but he would do those things when I was home so it wasnt really out of the ordinary (typical Jack Russel stuff).

I got him a safer crate, one of the plastic ones with a small metal gate and started crate training again. He is okay in it while he has his peanut butter kong but then wants to come out, he wont freak out like when he was young but he will let me know. I tried tether training too but its the same problem with the crate, he will cry and bark if he cant get to me, even if im 2ft away. It doesnt matter how or where I leave him he just wants to be able to get to me. So its not really a confinement problem, he will actually go in the crate on his own sometimes now. I started leaving the crate in the bathroom with him and just leaving it open and gradually he stopped panicing and trying to run out of the bathroom when I would leave. He started going in the crate obediently and would sit calmly while I shut the bathroom door to leave. I thought we were making good progress! But something changed one night after I went to the movies for 3 hours, he has been alone for that long plenty of times but after that night he started trembling and shaking when I put him in the bathroom to leave. I feel like Ive lost all progress and dont know what to do now. Should I start from square one or consider medication at this point?

Hes and amazing dog in so many other ways, he was potty trained after like 48 hours somehow, he has no problem self regulating with naps throughout the day, never aggressive towards other dogs or people, incredibly cute and acts like everyone is his friend, hes done really well in puppy training classes, and he alternates between being an absolutely hilarious psycho and a sweetheart but thats just his breed. I love him to death and would never consider getting rid of him, but the separation anxiety is the one thing I just cant figure out.