M.P.
I suggest that partnering would only add a different layer of stress. With a partner you won't be in control of everything. Even if you know the partner well enough that you think you can trust him, you still have to stay on top of everything so that you'll have a partnership. With a partner, you'll have to discuss plans and make decisions together.
I suggest that you and your husband talk together to see if you can describe what is causing the stress and then together find a way to alleviate the specific cause of stress. If it's your husband having to deal with tenant issues, perhaps you could take over that part of the business or you could hire someone to deal with tenants. If it's maintenance that is causing the stress, perhaps you could hire someone to do some of that.
If the building is not earning enough money to hire help then perhaps you need to raise rents. Perhaps you need help with a more efficient business plan. Have you done any reading or taken any classes on property management. Perhaps consulting with a property management firm would be helpful.
Is this building your main source of income? If your husband works full time managing the building perhaps working for someone else would enable him to hire more often.
I suggest that you need to take a closer look at a bigger picture. I do not see having a partner as being of any help unless you need the money a partner would provide. However, finding a partner is in itself quite stressful and would require legal advice. How would you know if you could trust this person? How would you know that you could work comfortably with this person? How would you know if this person has the skill or knowledge to be successful in business?
Or are you thinking of only having a partner for the money he could provide? If so, how would you decide how to share your income? Would his money enable you to make more money from the building. IF not can you even provide a return for their investment.
I strongly urge you to talk with an attorney about the details of a partnership. It's not an easy thing to set up.