He would call me, ask me to attend work parties with him, go to movies, come over and 'hang out' and show the tell-tale signs of jealousy when I'd consider dating someone else. We would spend Holidays together with his family, go out to bars together... but he wouldn't ever 'date' me.
I finally tired of this routine and started slowly exiting his life and for six months I didn't hear from him. Suddenly he called me out of the blue and started inviting me to do things two and three times a week for about a month and was acting completely different- extremely Happy, Confident - so different in fact that I commented on it a couple times to him before he told me that he'd been seeing someone else for 6 months. He crushed me at that point, and I hated the fact that he'd deliberately pulled me back into his life for God knows why when I was moving on and doing fine without him.
Things have not been the same with us since then, but I finally realized not to waste my time waiting for him. I just wish I'd realized it a lot, LOT sooner. Its so hard to describe how days became weeks, months became years... and all the while thinking I was being 'patient' and giving him the space he needed.
I don't know your crush, and only you can make the call on how much time invested is too much time... but if I may offer some advise, set yourself a time limit and stick to it. It won't be easy because you'll feel that you've made 'progress' with him and don't want to have all that effort be for nothing... but the longer you wait, the harder it will be to walk away.
Its the proverbial person at the checkout line. The longer you invest your time into waiting, the less likely you are to walk away.
You'll be doing yourself a huge favor by determining up front how long is 'too long' and abiding by it.