I have been really enjoying spinning on the flats, hills, etc lately. I have a triple and NEVER use my 52, never. it is hard for me to push. I am always in my 42x17-21 just spinning 95-115rpm. it feels more natural to me and is much more comfortable. when i try to push my big ring my quads start to give out, burn, and I lock up which takes 1-2 minutes to recover from riding slowly

Am I going to be losing leg strength/size by spinning and using my aerobic system more? My aerobics will go up I betcha but my leg strength will probably go down. it only seems logical

No, spin away. Climb more, go faster. Do sprint intervals.

I never train intervals. just hills/hill repeats. I am new to cycling so bare that in mind So hills will still keep leg strength?

No, but you will have to put in the grunt work later.
You are still in the process of building base miles, developing a high cadence style early on will pay benefits in the long run.Your 42/17 gives 65GI, a bit short of the ~70GI we used for winter fixed gear training but far preferable to slapping it in the big ring and grinding along as many new riders are wont to do.

Riding distance builds endurance, riding hills builds strength & doing sprints builds speed. Just coasting along after the summit is a waste of momentum, get on with it and build momentum for the next climb. Your big ring is for the downhills while getting base miles in to maintain a high efficient cadence and have enough gear under your legs that you are not dangling from the saddle at downhill speeds.

This is where the work comes in, ease into it but one must do the work to become proficient, or not. Intervals come next & time trials.
Your choice.

A well selected gear range is one that is as tight as possible for efficiency with a low enough to climb the biggest ascent in the area w/o undue stress and as big enough gear to fly down-wind-down-hill w/o spinning like a hamster in a cage or plodding.

-Bandera

Thank you so much for the insights! All advice will help me. i have been cycling only for 2 years

Seriously, join a club, get a coach and start a program.

"Get the most out of that gear" was a core concept of my 1st coach.
Developing a supple powerful high cadence style w/ grunt & spin on demand was the foundation "back when".

-Bandera

Supplesse, toujours supplesse.

I have no idea what that means.

Train your weakness. If you are climbing a steep hill you will need the leg strength. I have the opposite problem as you. I try to do one high cadence ride per week.

It sounds like you don't have a lot of strength to lose. Keep up the spinning but try and do some high gear, lower cadence work from time to time.

Everyone's different but IMO spinning up to 115 regularly on a bike with multiple gears is a bit excessive.

OP
If you do hill repeats by spinning up hills in your easiest gear, than you are probably not getting significant bang for the buck for them. Hill repeats are something that you repeat to failure, with the goal of fatiguing yourself. If you don't get there, then you aren't getting there.

If your goal is to be the fastest possible, you need aerobic strength and leg strength. Sometimes, it makes sense to mash, some times it makes sense to spin. On a long hill, spinners win, on short hills, mashers usually come out ahead. Be able to do both.