Probably no one would like to be in a situation where someone confesses their love, and you realize that this relationship is casual or that you do not love this person.
What to do? First of all, don't let feelings like embarrassment, awkwardness, or pressure from your partner take over you.
Saying "I love you too" when it's not true is at the very least unfair to the person.
Instead, be yourself and tell the truth - this will be the greatest manifestation of concern for the person who confessed his love.
Be gentle and tactful, respect the other person's feelings, and try to soften your refusal with compliments and humor, if appropriate.
For example, you can say: "Unfortunately, my heart is already taken by another love", "I don't deserve such a beautiful person!" or "I want to save you from disappointment. You just don't know me."
Explain that you are not ready for a relationship yet, as you have other priorities (studies, career, etc.).
You have warm feelings for this person, but you cannot promise more and are ready to meet or communicate from time to time.
If the confession comes as a surprise to you, explain the situation to your partner and ask for time to think about it.
For those who find it difficult to say no in person, it is worth taking the advice to send a correct and delicate message.