It's been 5 years since I have used a nitro powered rc.. Was wanting to get back into it. I have bad memories of replacing my engines every couple months. Just want to know if that was normal or if I was too hard on them.

It really depends on the make of engine and especially how it was run and stored.

Some of the best engines (like OS) will fail early f not ran properly and stored properly. If an engine has always sat with unburned fuel in the crankcase and if it has sat for months or years between runs then the bearings will almost always fail early.
If they are tuned to run lean and at high rpm's then you can guarantee a failed connecting rod bearing and conrod breakage and/or early piston, ring, or liner wear is in the near future.

Typical RTR engines last up to 4-5 gallons max with modest care and abuse. Expect the same from an OS, honestly. Maybe more with better care - good fuel and carb setting is paramount. Some guys report 12+ gallons from the Italian Engines - Picco and Nova and their re-brands. Nova is more affordable than ever before - AND they’re stupid powerful and easy to operate.

So as said - quality of the engine will play a role in the lifespan as does the care and operation.

A couple of months? Who can afford that? Flyinwlenda mentioned stored properly. I only used electric motors in cars but my planes used fuel and lasted years. I always ran the engines dry the last day of the weekend and put in a few drops of after run oil.

Car engines are run in a completely different environment using different fuels and much harsher throttle control. Airplane engines last forever because they’re not beaten like a red headed stepchild at 35,000rpm constantly. Add to that the fuel for cars is only 8-12% oil on average, the margin of error on needle setting is much much narrower. Run a car engine lean a few times and it’s toast.

It depends on how are you going to take care of it. Routine check up is a must. A car buyer or car owner should be aware of how to take care of engine.