Be direct
Tell them in a straightforward, non threatening way, making it clear that you understand if they don’t feel the same way.
Examples:
“I have strong feelings for you and would like to be more than just a friend to you, but I totally understand if you aren’t interested in me like that.”
“I have a confession to make. I really like you. Like, really like you. But if you don’t feel the same way, I totally understand and will always value you as a friend.”
“I’m very attracted to you and I hope things won’t be awkward because of that. I’d be super happy if you felt something for me too, but if not, everything is going to stay the way it is now. I just wanted you to know.”
Share your concerns
Moving from a friendship to romance can create some obstacles regarding your friendship. Be clear about any concerns you may have.
Examples:
“I really like you. You’re my best friend and I’m not sure how my feelings might affect our current relationship.”
“I love having you as a best friend and I’m unsure if these romantic feelings are worth losing that.”
“I’m concerned that a shift in our relationship might mean that I’d lose you as a best friend, and I don’t know if I want that.”
Ask questions
Ask them about any concerns they might have about going from friendship to romance. These questions are only relevant if they are considering entering a romantic relationship with you.
Examples:
“How do you think this might impact our current friendship?”
“What do you think will change if we take our relationship to the next level?”
“Do you have any concerns about losing our friendship if we were more than friends?”