I think you didn't cross a line at all, it's a wonderful thing to tell your therapist about how you are feeling about them at the moment.
Those feelings can change--fluctuate--and tracking those changes can be revealing and useful.
You can talk about anything you want in therapy and how you feel about the therapist is a legitimate and potentially incredibly useful topic of discussion.
For example--if you start to feel angry at your therapist, sharing and talking about that is great.
And sharing loving/close feelings is great too.
Most people who go into therapy --and perhaps most people --have issues in their relationships with others and sometimes the most productive way to move forward with those is to examine the relationship that is right there in the room.