If you carried over a romance from ME 1, the relationship carries over into ME 2. But your love interest will not join your squad. You will see their picture in your cabin. It is possible to pursue someone in ME 2. In this case your love interest's picture is turned upside down.

Mass Effect Wikia says if you do this it does have an adverse effect on your relationship in ME 3 if you wish to pursue the same love interest.

If you carried over your romance with Liara from ME 1, the relationship carries over into ME 2. But your love interest will not join your squad. You will see their picture in your cabin. It is possible to pursue someone in ME 2. In this case your love interest's picture is turned upside down.

Mass Effect Wikia says if you do this it does have an adverse effect on your relationship in ME 3 if you wish to pursue the same love interest.

EDIT:

Reaffirming things with Liara will not affect your chances with Kelly in ME 2.