Having been a middle-market commercial lender at what is now Bank of America, I can assure you that talk of wanting a "relationship" only means, "We want as much of your business as we can get, but only to the extent and for the amount of time that it suits us."
I've had to tell 20-year customers with impeccable credit and financials that their $10 million loan relationship had to be moved elsewhere by next year simply because they were in the wrong SIC code (that is, the bank was exiting lending to it, regardless of the numbers). The bank will spend a decade building that "relationship," and then they'll flush it -- instantly.
For the bank, a relationship means that we have it all...deposits, loans, credit cards, merchant services, your personal mortgage, your investment accounts (what we called "share of wallet")...the whole shootin' match, and while increased profitability is one reason, the other is nothing more than that they can mess something up and still be less likely to lose the customer. It's just too complicated to undo everything when they have you all sewn up.
I would never recommend that anyone give all of their business to one bank. You should always have another one in there, competing for business, keeping each other honest.
Also, be careful about where you keep your deposits. Having them at the same place you borrow can lead to surprises (see "offset" for more details).