直接告诉对方你觉得双方可能不太合适做恋人，但希望还能继续保持现有的友情。如果对方不愿跟你继续交往，那也不用太强求了。
I like you, but I'm just not interested in you in that way.
我喜欢你，但我对你的感情不是那种恋人情感。
You're a great friend, and I'd rather that we keep it this way.
你是一个很好的朋友，且我希望我们能继续保持这样。
I'm not the right guy/girl for you, I hope that you can understand and that we can still be friends.
我不是适合你的男人/女人，我希望你能够明白，且我们还能够继续当朋友。
I like you as a friend, and I hope that we wouldn't have to give up our friendship over this.
我喜欢你，但只是作为一个朋友的感情，我希望我们不用因为这件事而需要放弃咱俩的友谊。