How can I fix this side of my bathtub?

My guess is to caulk it with a caulking gun and some caulk. You can buy at a local home Depot or housewares/Home improvement stores. A good store will give you more specific details and advice.

We had one just like that, but it popped out when you sat on the side of the tub. This is because the side was not reinforced to handle the weight of people sitting on it. We resolved our problem by never sitting on it there, but only close to one end, and only entering the tub from the end.

I don’t think caulk (or even superglue) will hold that. You need something with some real strength, probably some form of epoxy. Make sure you get one made for plastics ;)

I agree with @jerv that you need some super duper adhesive to fix it, if it can be fixed. Strong adhesive and clamps to hold it together while it dries.

If it is popping open because there is water or mold in between the pieces that would have to be corrected first. Most likely it’s just poor design or cheap materials.

Wondering if you could run some sort of trim along the top and sides? I’m going to forward this to my mechanic people.

From a friend on FB: ”Don’t glue it! That’s where all of the plumbing for the jacuzzi tub is. If there’s ever a leak you’ll have to tear it all apart to fix it. I would suggest tension fasteners. You can get them at Home Depot or Lowes. A metal stud affixes to the cover and the tension catch to the inside. It’ll pop right in place and hold shut.”