When I think of trust, however, it usually has more to do with the stuff that leads up to the cheating. I've been cheated on before, and I've been hurt by it, but more because it was a sign that the person I was with didn't trust or respect me enough to bring up the issues they had with the relationship before they went looking for something else. That's the kind of trust that I think is important, and also the kind of trust that's really hard to find. Tell me when I'm pissing you off, tell me when I'm being too clingy, tell me if that hot girl who hit on you in the club was a temptation -- no one wants to hear that , and it will possibly lead to an argument, but it's a of a lot better than hearing about it after it's too big of a problem to solve.
That's why the friend thing seems like such a non-issue to me. I would hope for, and I would work towards, a relationship in which I would know whether or not there was cause for alarm. I wouldn't have to suspect. Or wonder.