It makes absolutely zero sense for my dude, who has shown negative interest in Monica to suddenly be in a painfully uncomfortable situation with her at the end of this episode.
I think it makes sense, irrespective of your intentions. They have a connection and at the very least will have a growing friendship due to their mutual lose - his mother, her best friend.
It was something they did when he was a kid, she being a little drunk still and with her feelings all over the place has got nostalgic. He, as a good guy, does not want to hurt her and probably feels a little nostalgic, even if it's for a mother figure and a safe place and for him one of those safe places is watching TV with her in her bedroom.
For her to start stripping down is a bit cringy in in the context I've given, but you have a choice to try and help or not (presumably you'll fail). Before you have the option to wear PJ bottoms.
Even without the full analysis, MC wants to keep the mother onside at the very least or else he'll be in the same situation he is with Elaine, except without any legal claim.
ETA - welcome to F95 and your first like \o/
-----
Not at you, kibbles, but at those complaining about not knowing repercussion of choices....curl up now and hide under the bed...because real life is coming for you and you know what...you don't know, sometimes until 20+ years later the repercussions. The joy of games like this, you can jump into the dev console (I found out how with a little searching), you can save at multiple points and go back to them, hell you can even start over if things go that bad. I had forgotten the situation between Katie and shit 4 brains, so you know what I did? #shock horror# I went back to an earlier save... O.O