Sounds you're "pot committed" ... stay the course. If $$ is an issue then rent the guest house for a couple/few years. Perhaps a divorced friend/family needs a place to hang their hat. Throwing in the towel (selling) is not an option in my book.
Yea, I'm going to have to see this through. Just wondering, how long do you stay in a house before it makes any sense to sell (if ever)?