shiloh, I have to agree with keepingit. First of all, I don't think your houseguest wrecked anything. You all were obviously having problems...she just brought the problems to light.
Second, if you are serious about making a go of your marriage with your ex, you need to get rid of the bf. Even though you say that he's more like a roommate, you're still calling him bf, and he's obviously still acting like one (throwing fits because you're spending time with the ex).
Personally, I think you need time for you. Get rid of the bf, and take time out for yourself. You may find that you don't want your ex.
Me - 48 (at time of 1st bomb) H - 43 married - 16 Jul 94 no children 1st bomb - (said he was leaving) - 3 Jun 06 2nd bomb (said he was ready to file) - 10 Nov 06 H filed divorce - 17 Nov 06 Divorce finalized - 20 Jul 07