Since you’ve only been dating for five months, I think it’s best not to make a mountain out of a molehill. If you let this go, you’ll seem confident and sure of yourself, and that can bring the two of you closer together — if you don’t, and you make a big deal about it, it can have the effect of driving them closer together, and you don’t want that! Also, with any luck, he’ll get better, leave rehab, and she won’t see him when she goes to work any more. So, keep it drama free and take the high road.