Asalam wailkum Istella. I/we welcome your question.
As muslims its part of our faith that we dont just say or believe in almighty god, but we also believe that none has the right to be followed, obeyed, worshipped except God.... Why? simple.. because he is our creator, we exist, we are here because of him. So its only logical to live life correctly in the way shown through his book and messenger.
In order to gain the pleasure of allah we need to follow his commands even if they may go against our natural, innate desires. The desire for drinking alcohol or gambling, or even something basic as cheating, we may have these feelings but as servents of almighty allah... we have to control these desires and restrain ourselves, this is what leads to spiritual development. So at times this restraining and controlling of our desires also extends to our feelings of love. Allah says in his book, the believing woman (muslima) are for the believeing man (muslim) (and vice versa), and that it is better to marry a believeing person (ie a muslim) even if they be a poor.
Why? because allah has put higher rank and status in those who follow him and his prophet, and allah loves his believers more than the disbelievers because the believers have great love for allah and his prophet within their hearts.
Furthermore encouragement is given by the almighty, he says in surah nazi'at 40-41: 'as for the person who feared to stand before his lord (in the hereafter) and restrained himself from (unlawful indulgence in) lust, Lo! Paradise will be their home'
So in summary, its not permissable for a muslim/believing women to marry a christain man and we are directed by allah himself to marry fellow believers in faith, and the verses above i mentioned, we see allah encouraging us to safeguard our imaan and religion by marrying believing partners even though we may be attracted to people of other faiths.
In this life our imaan/faith is tested in many ways, even our feelings of love for allah is tested, as one of the companions had great love and honour for his mother, and this mother loved this son of hers the most. When she heard he became a muslim she went on hunger strike until he gave up islam, the son pleaded to her plz eat, u will get sick. So here, we see allah was testing him with the great love he had for his mother, to see which love is more.. for his mother/creation OR for his lord/the creator. In the end he said to the nearest meaning, even if u die many times over i will not renouce my religion, and she gave in. So hence he was successful in this test. So i hope the sahabi story and the verses of allah encourages you to make the right decision, after all life is short and the meeting with our lord is fixed ahead of us. You and other brothers can give him dawa, encourage him to study the quran and to upgrade to islam ... however if he merely converts so that the marriage can go ahead then this is a false shahada, and allah knows best.
ElaqhEqah.