Is my fast valid even though I fasted without performing ghusl after my friend (lover) kissed me on the day prior?

First, you must repent to Allah, because establishing a friendship between a foreign man and a woman is not permissible. As for mere kissing, it does not necessitate ghusl (ritual bath). If ejaculation occurred and you did not perform ghusl, that does not invalidate the fast of the following day or the current day. However, disobeying Allah while fasting diminishes the reward and may completely negate it, as the Prophet, peace and blessings be upon him, said: "Whoever does not abandon false speech, acting upon it, and ignorance, Allah has no need for him to abandon his food and drink." So, if the sensation means ejaculation, then you have become in a state of janabah (major ritual impurity), and your prayers before performing ghusl are not valid and must be repeated.