How do you stop? 

This is the only relationship I've been in that I haven't cheated. I haven't even flirted, really. It's been over a year. I had no impulses even until recently. My partner and I have had a few problems recently, mostly stemming from his occasional lack of empathy which stems from his ASD. but it's really had a large effect on how I view the relationship. 

And suddenly I find myself with a crush. Whom I'm suddenly obsessed with. Thinking about him way too much. He has my number but I don't have his. And I'll definitely see him a few times a week just by where we'll both be. I mean, I don't even know if he's interested in me. He's likely not. (Has my number only for semi professional reasons). But I've been hoping he'll text me. 

I feel torn in half. I don't want to destroy the relationship Im in, I value it and I really love him and see some sort of future and I definitely don't want to hurt him. But I also split when things are even mildly rough.

 But the impulse to flirt etc with someone else is overwhelming. Completely. I keep telling myself it's not worth it. But the desire won't stop. 

I'm scared of making mistakes. I'm terrified.