If I was falling in love with a non Christian, and it is mutual, what advice would you offer me?

Naturally , Its Not our Place to Tell You Whom You Should Love or Not , But If that Really Happens ,,,,,,,,,, I will Say "" Love is Blind "". Nothing Else !.

Watching a testimony in Taiwan in which the lady used to go to church when she was young later she met a man he loved her and she loved him they got married and later they got baptized and go to church together

Move on, God has a better plan.

Be not unequally yoked together with a non believer.

What is your definition of love? Are you speaking of Scriptural love or are you speaking of attraction? If it is attraction, then falling in attraction is self explanatory. It is no different than a piece of rust being attracted to a magnet, and then once it is there, it is stuck to the magnet.

If you are speaking of Scriptural love, then that is a decision/choice/action, and you can choose that for/with anyone.

My advice would be not to just write it off. Paul tells us that unbelievers who naturally obey the commandments are more righteous than "believers" who do not (Romans 2). I would say find out why he is not a believer, and then give it some time to see if your influence brings him to faith in the Messiah.

To the contrary, if he is a hardcore believer in another religion, then you are at fault, and your irresponsible choice to pursue it from the beginning will have consequences.