This is a nice one. I wish the original Maria-sama Ga Miteru had more true lesbian romance. As much as I like that series, it got a bit frustrating that none of the relationships went beyond subtext.
They both love each other very much. Sei does not have to worry. Shimako loves Sei in the same way. I am sure that they will understand that they feel the same way about each other.
I remember this was one of the first yuri couples I remember so long ago.
Sakura and Tomoyo were the first! I learned love can manifest itself in many ways. Be happy and loved dear ones!