I'd start by asking whether the unknowns of the problem are primarily social and psychological, or whether they include things that the human intuition doesn't handle well (like large numbers). If it's the former, then good news! This is basically the sort of problem your frontal cortex is optimized to solve. In fact, you probably unconsciously know what the best choice is already, and you might be feeling conflicted so as to preserve your conscious image of yourself (since you'll probably have to trade off conscious values in such a choice, which we're never happy to do). In such a case, you can speed up the process substantially by finding some way of "letting the choice be made for you" and thus absolving you of so much responsibility. I actually like to flip a coin when I've thought for a while and am feeling conflicted. If I like the way it lands, then I do that. If I don't like the way it lands, well, I have my answer then, and in that case I can just disobey the coin! (I've realized that one element of the historical success of divination, astrology, and all other vague soothsaying is that the seeker can interpret a vague omen as telling them what they wanted to hear— thus giving divine sanction to it, and removing any human responsibility. By thus revealing one's wants and giving one permission to seek them, these superstitions may have actually helped people make better decisions throughout history! That doesn't mean it needs the superstitious bits in order to work, though.) If it's the latter case, though, you probably need good specific advice from a rational friend. Actually, that practically never hurts.

I just came out of a tough Major Life Situation myself. The rationality 'tools' I used were mostly directed at forcing myself to be honest with myself, confronting the facts, not privileging certain decisions over others, recognizing when I was becoming emotional (and more importantly recognizing when my emotions were affecting my judgement), tracking my preferred choice over time and noticing correlations with my mood and pertinent events. Overall, less like decision theory and more like a science: trying to cut away confounding factors to discover my true desire. Of course, sometimes knowing your desires isn't sufficient to take action, but I find that for many personal choices it is (or at least is enough to reduce the decision theory component to something much more manageable).