Doc and Marie

I don't think either.

I think Doc saw Marie as a young version of himself before he had to leave medical school to marry Lola.

Marie was smart and talented, he was worried Turk would end up causing Marie to "have to get married" as well. She reminded him to much of his own past.

Doc was stirred up by Marie. Reference the scene when he retreats to the bathroom and smells her lavender-scented salts, which he had mentioned to Lola before...

Oh, I think he was turned on by her. He was so adament about not taking in a boarder, but the minute he meets here, all he can do is stare and agree like a man hypnotized to give away his wife's sewing room to her! There probably were some paternal feelings mixed in there, too, but his concern about Turk seemed more from jealousy than from wanting to protect her.

Looks like I picked the wrong week to quit sniffing glue.

He most definitely feels a mix of paternal protectiveness and sexual attraction toward her. This internal conflict is what sets his confusion and eventual alcoholic relapse in motion.

Yes. Marie was flirting with Doc. There is a scene where Doc kisses his wife goodbye and Marie asks if he can kiss her, too.