Deciding factor on who he marries?

I think it's the most neglected...

I neglected Ysolte and she remained forever alone as I planned. I wanted Mina to marry him, I helped her but was rude to her.

o-o well I picked all the choices for Cecilia and those were sure fire negatives...Ysolte was just neh....didn't care. and I wanted Mina to stick around so helped her the most. She goes on to say she's a fool for chasing him.

I got in bed picked many choices related to Cecilia and Keane decided to get in bed with Ysolte.

I THOUGHT talking to Cecilia was a decisive option, but I accidentally made her mad (I wanted her to stay as an NPC), yet she still ended up staying as an NPC as I had hoped.

Well I pissed her off ignored her a bunch of times.