Gemini,
Here's my 2 cents - if it matters... first, read my post "a functional alcoholic" below yours and see what GingerM had to say to me. i think it would apply to you as well since we are in the same "detachment" boat.
Second... I think for me it is the holidays that are making me feel like I have this duty to allow my dad back in. It is sad to see him hurting to see his grandkids (my kids) at Xmas, but like my friend said, it is one holiday, one day. is it worth my mental health for the rest of the year? I answered no. Everything I told my dad when separating from him remains true. Is this also true for you? Do you feel the same way you did 5 months ago? You said you were much happier now - so I suspect so...
Your main goal should be for you to be happy. We have but one chance on this earth (that is what i believe at least) so why might as well make it the happiest, best one we can and if that means cutting out negative infuences that make our lives anything less than better for being in them, then I say its your right.
Anyhoo, I just wanted to let you know that someone out there feels your pain and I know EXACTLY how you feel at this moment. Anytime you need to talk - I am here...