My partner, Wil, and I have only done non-gay-specific cruises. So far we' ve been on 6:
Seabourn Sun-Capetown-Las Palmas
Radisonn Navigator-Canada (was to be Bermuda but Hurricane Fabian changed that!)
QM2-Maiden Southampton-Ft. Lauderdale
We've never experienced any troubles being a gay couple. We don't hide that we're gay nor that we're a couple. On all of our trips we've made good friends be they gay/lesbian or straight, young or old, (we're 40 and 47), passenger or crew.
Oddly enough, we've only been to one FOD gathering on a ship, and that was the QM2. Other than that, any people we've met regardless of sexuality, we've met as part of the normal course of a day.
As you'll see, the ships ranged from mega sized (QM2) to small (Seabourn Spirit) and again there were no issues nor discomfort for us.
You and your partner will naturally gravitate to people you're comfortable with and they to you.
Remember...the important thing about a cruise (like any other type of vacation) is to ENJOY YOURSELVES!!
By the way...what cruise are you two going on?