My Boss Fired Me While On Medical Leave For Surgery. My Boss Set The Requirements For Me To Return To Work And Then Says My Recovery Took Too Long.

Location: Nebraska A little back story. 4 years ago I tore a tendon in my elbow and it wasn't work related. The doctor gave me 2 options, surgery or cortisone as it was mild. It was the busy season for my job and I was already going to be short 1 employee who needed the summer off for surgery and there was no way I was going to leave my boss hanging, so I took the cortisone. My fault I'm aware now. Said employee never had the surgery (important for context) but still took off 8 weeks, came back to work with same schedule as before, as if they never were gone. Fast forward 4 years, my elbow it's completely destroyed and I need a major surgery to fix it. I have 10 days notice and let my boss know and I make an attempt to get as much of my shifts covered for the next 3 month thinking that's more than enough time to recover. My surgery ended up being a bigger deal than I was expecting. My elbow basically was cleaned completely out and rebuilt. No soft tissue left from the cortisone, I had both nerves released, nerve damage repair in mid forearm, and carpal tunnel release and repair I also received 2 screws to hold things together. I was in a cast for 8 weeks and had to start physical therapy to slowly stretch all the new tendons. I made my boss aware it was going to be more than 3 months due to the extent of everything. My boss tells me he wants a 100% full release with zero restrictions from my doctor before I can return to work. My doctor said that could be up to 18 months. At 16 weeks post surgery I get a partial release with 5lb weight limit and 4 hour shifts do to the constant use of my elbow/wrist/hand while working. My boss says I'm getting there and keep on working at it. He also told me that we don't ever schedule 4 hour shifts. But we do. I practically begged him for any hours. Im almost 6 months post surgery with a 100% full release after my last therapy appointment in 2 weeks and I let him know that I was expecting to return to work. He then that he didn't have any shifts or hours for me since they had to hire a person to fill in my shifts and he wasn't going to take her hours away. He then informed me that open heart surgery only takes 6-12 weeks for a recovery and he thinks I've taken too long. He has assured me several times that I was still employed throughout this entire ordeal. I do have all of these in text from him. Is this legal?!?