While there is a strong romantic connection between them, their relationship is complex and filled with uncertainty, especially due to the war and their differing roles in it.
In episode 48, Lacus sings "Beyond the Time," a song written for Kira that expresses her deep feelings for him. While it's a powerful moment and some interpret it as a proposal, it's not explicitly stated as such. The episode focuses more on Lacus's efforts to end the war and her desire to build a peaceful future with Kira.
Their future is left open-ended, leaving room for interpretation and fan theories.