Everything is a risk, but you don't want to get to 90 and think "damn it, I should have done that business".
The worst thing that might happen is you might run out of cash, give it up and get another job. Or someone will rip you off (be it a biz partner, investor or rival) and you give it up and get another job. It's stressful and not fun, but you're not going to die if your startup fails.
Just to clarify, I (gladly) fell out of love with my idea and dont so much worry about people "stealing" it. I'm more worried about a business partner building an "escape hatch" in the partnership contract and screwing me out of ownership/stake. Not sure if that changes your answer or not.
Of course protect yourself. Have a contract. Never go with a vague contract and then hope for the best. Have everything in writing. Ownership stake, expectations an escape hatch for either of you in case of a falling out etc. For us there was a clause stating that the contract could be nullified by either party within the first 90 days for any reason.
I had worked on my side business for 3.5 years at the point I partnered up. My partner first spent 2 months working away and we didn't formalise the agreement. We were making sure that we were going to work well together.
I finally said that we can't go on like this and we really need to formalise his ownership etc. We discussed figures and arrived at an arrangement that worked for us both.
In the end, for me it came down to this: own 100% of 0 or X% of a real business.
Once that clicked for me, bringing on and trusting a partner was an easy choice.
I assume the risk of not succeeding to grow your business and the risk of succeeding but you deciding to dismiss my work and not compensating me. No contracts, only verbal agreements to start off.
I've done this kind of deal twice before with moderate success in both. If you are interested, email me (on my profile) with more details about your product.