Attraction involved a lot more than Alex would have guessed but so did romance. Just because you were in love with someone didn't necessarily mean you got to be in a romantic relationship with them. That was dating, which could lead to being married.
Or in Ray and Heather's case, jumping straight from friendship to being engaged because they already knew they were compatible. Dating was meant to help determine compatibility.
He already knew that he and Claire were emotionally compatible so did that mean they should get married? He did want to stay with her for the rest of his life and that would certainly do the trick.
"So what you're saying is that because I'm in love with Claire and already know we're compatible emotionally that we should get married," Alex surmised.