Good for you on finding an exercise activity you love. I tell people, the key to sticking with something is to find what you love. Thus, you will seek it out, and miss it when you do not have it.

I'm an instructor , as well. Going hard at it this winter I'm pretty tired, and over-trained. Got some things hurtin on me, owe lol. I've had 6 spin classes a week between my two gyms. Just let go of some. I love what I do. But, man am I glad. Also, I road cycle and mtb.

My issue I have with cross training is that pedaling is pretty much the only thing I can do. No impactive exercise for me per the doc. I hate walking. It doesn't cut it for my heart rate. I also kinda hate the pool. Never could get the stroke with my asthma. See remark number one about sticking with what you love lol.

Strength training is good. Maybe try to focus on working those muscles you are not getting in Spinning. Also, make sure you stay fit correctly to your bike. Any signs of pain/discomfort back it off. Stretching / core work is always good as well.

Good Luck.