What I tell my clients if they feel romantic about me, and tell me so, is that those feelings are normal and OK to feel. I assure them that I will never take advantage of their feelings and will always only have a therapeutic relationship with them, and always in the office.
Depending on the client’s response, I might encourage them to talk more about how they feel. I tell them that they are only seeing the very best of me when I am totally focused on their needs and how to be of use to them, and that they may never have had something like that before. I emphasize how they are only seeing me for an hour a week ( or whatever it is) and I am careful to meet with them when I am fully able to be present to them and helpful. If I am tired or sick I cancel the appointment. In this way I am purposely telling them this is not a normal relationship, but a very special one that often includes the person who is the client developing strong feelings for the therapist.
Clients usually find the romantic feelings for the therapist dissipate as they outgrow the need for therapy. They may always feel a fondness for this person who helped them, but the intensity goes away.