I just feel so stupid, I should never have let him come here.<
Rose, no need to feel stupid. You tried it, it did not work. You know not to try it again. That is how we learn. When he is gone, when you feel well, you need to start thinking of what do I do when I am ill/feeling low strategies. So, how do I deal with things differently next time? That is all.
To his comments on your house: I read something recently which said that FWs (it did not use that word) will attack the things you most value. If they criticise what you love, you defend it automatically, and as soon as you defend something, you sound guilty, you are undermined.
What he is doing, when he comments negatively on your house, is commenting negatively on your choices, on something you have worked hard to attain and which you should rightly be proud of.
If he stays in your life, it will not be long before he is commenting negatively on your course, your day-to-day work patterns, your assignments, and undermining you there too.
Do not start seeing your house through his eyes. Do not see your life through his eyes.
My personal recommendation would be if his dad is coming to see DD, then they can go out to the park. Any future contact is not in your home. Start setting boundaries.
I got a long letter too, I filed it with my solicitor because of some of the content, and then never saw it again. In other words, ignore. Do not even begin to engage.