Dat feeling when you successfully standing overhead-press 92kg / 201lbs a couple of times with beautiful form. I never get tired of it. 

And If I imagine I'm in a medieval battle and I'm actually picking up and lifting an armored opponent instead of a weight its feels even cooler.   

I have several degrees in shoulder pressing.
Most likely you are using too much weight, what happens is your shoulders alone are too weak to press the weight so you lean back to incooperate your upper chest muscles to press it. Like a standing bench press. 
You might not even notice that. What happens is you arch your back and you squish the discs which causes a LOT of damage very quickly. 

If you shoulder press a weight, once the barbell reaches eye-level immediately pull your head through the window your arms create to ensure the barbell goes straight up above your head and you are not pushing it away from you.

In other words, NOT this: 



As you can see this gentleman is leaning like shit in order to ''shoulder'' press a weight which his shoulders actually cannot handle. Its practically a bench press while standing. 
Note how his head is way behind the bar as he presses it. That allows you to press a lot of weight but it grinds the discs of lower back into oblivion in no time at all. 


There is a way to shoulder press weights where it is impossible to arch your back / lean, its called the Z-Press, named after the best shoulder presser in the world.
You sit flat with your ass on the floor, with your legs straight, slightly v-shaped, and you do normal shoulder presses with the bar. If you arch or lean just a tiny bit you'll fall on your back. 
A great exercise to target the shoulders, increase balance and to teach you the correct form. 

I need to workout again cuz I'm getting fat around the middle.

I used to not exercise as much, but ever since I started watching through all of the classic superhero shows from the 90s and early 2000s, I've realized that being out of shape is no fun.

I might not be Batman, but at least I can avoid becoming the Blob.

The muscle can't regenerate the damage it received from the last training. If you don't give the muscle enough time and rest to fully regenerate you'll become weaker. 

I hope you'll find the discipline to pull through, 5 days would be good split. 

If I go there straight after work, then I'll feel bad if I leave right away and for wasting money on a membership.  I'm going to make myself turn it into a habit, even if I have to writhe around in agony on a treadmill.

I've always found you have the right mindset for sports, compared to most other people, you'll succeed.

You have to learn to love it to make real progress.