listen dear, first of all lemme make u very clear with the fact that there is no such rule that a national(qatari) cannot marry an expat. so there will be no difficulties in matter of government.
as about converting your religion, its good if you agree with the religion of your guy and are ready to believe in it, but hamdulillah, islam is a religion which does allows a muslim man to marry a christian or a jew girl.
and as about you said that he havent yet even introduced you to his family, then i would also like to add that its not necessary for the family of a guy to interfere in his this personal matters (after he is matured), he has the total right to marry anyone even if it is against his family wish, but none theless he is supposed to provide you with all your rights being his wife and has to fulfill his responsibilities and duties towards u.

but as you said that this man already told you that marriage is not possible in your relationship then i dont understand that why on earth are you still stuck with him! its very clear that if he is not gonna marry you then he is only playing around with you, fulfilling all his desires.

though being a muslim, i would suggest you to get out of this relationship because as you said that the man is not ready to get married, then you are just wasting your life behind him and he is doing nothing else than increasing his sins, to which he will be answerable to the Almighty.

Peace be upon you.