Now I see it.

Every relationship cools a little eventually. It's just something you have to understand and allow for. But for me, there was a voice in my head saying that as soon as there was a commitment, the love my partner felt for me would fade and vanish. Like it did with both my ex-wives. With my girlfriend, everything that brought us closer freaked me out. I saw superficialities like looks as more lasting than her love. I wish I had seen it sooner. I can't attempt a serious relationship unless/until I fix this.