I don't think there's anything wrong with believing it. But I think making absolute assertions can be a sign of naivete. I am unbelievably happy in the relationship with my girlfriend, and I am not the sort who is given to infidelity (as many are.) But is it possible for me? In being objective, I could imagine a scenario in which I was energetically pursued by a woman, and with a certain set of circumstances being present, I could succumb. But it seems more likely (knowing me) that I would find a way to sidestep this scenario. Is it possible. Yes. Do I believe I will? No I don't.
I think having been a Watchtower zombie has helped me in this way. For thirty-eight years I lived in a sort of virtual reality in which I often sensed my reality was not genuine. After my "awakening" I came to see that most everything was fake. Well, now that I'm out, I want things to be as real as they can be. I am free to discuss what I want to discuss, disagree with what I want to disagree with, believe in what I want to believe in... And when it comes to all of my relationships--especially the one with my lover...
I want real.
And I won't believe it is real if I am not treating it as real myself.