All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhiwasallam, is His slave and Messenger.
It depends on who the loved one is. If the loved one is not your wife, then it is totally forbidden for you to exchange words of love with her whether in Ramadan or at any other time, and whether you have proposed to her or not. This is because such an action could lead to immorality. Whoever does this is considered sinful and has to repent. However, such immoral behavior does not nullify one's fast.
However, if the loved one whom you refer is your wife, then there is no harm in saying words of love to her while fasting in Ramadan, provided that you can control your sexual desires and would not commit what is prohibited while fasting. Still, it is better to avoid such displays of love while fasting given that the perfection of fasting depends upon how much the fasting person stays away from all worldly pleasures. Your fasting remains valid even if saying love words to your wife causes you to discharge seminal fluid. In his book Al-Minhaaj, An-Nawawi said, “Seminal discharge nullifies the fast if it happens by masturbation or sexual contact. However, ejaculation that is caused by lustful looking or thinking about sex does not nullify the fast.”
Allaah Knows best.