I agree, as long as one doesn't become dangerously, blindly, trusting in addition to all of that forgiveness. Something like Angel told Connor. "You're my son, and I love you, now get the hell out of my house." Not EXACTLY the same thing, but close enough for an example, and she DID begin to learn that by the end of the televised series. In Season 5, Giles (rightly) killed Ben, not because Buffy would forgive him, but because she would then almost certainly lose all distrust for someone who she saw as no longer a threat. In Season 7, yes, she did forgive Spike practically the instant that she discovered that he had a soul, but she didn't bring him into her home immediately, she put him somewhere where, she fully believed, he would be unable to harm Xander because of the chip. Then, when she DID finally bring him into her own home, it was under restraint and careful watch. Spike didn't get full run of the house until several weeks later, once Buffy was as certain as possible that he could be trusted. Then, at the end of Season 8, she forgave Angel for being Twilight, but specifically said that she did NOT trust him anymore. Buffy's learning. It just took awhile.
I do wish that she would be a little more trusting of Faith, though...