How Do I Tell Him That I Can't Marry Him Without Hurting His Feelings?

Good day ma...
please I need your advice ma... Here is my story, thanks.
So I just turned 27 years old in September, I have been dating this guy for two years and six months now.. He is a very good man, a man I would love to spend the rest of my  life with.. He has no issues at all, my parents liked the guy and so okay with him being my man, and so we decided to take the relationship to the next level. 

So early in January this year we went to see the pastor of our church, because I was about leaving the country for my masters and we wanted to have an introduction done before I leave, and then come back December this year for the white wedding. When we went to see the pastor to tell him of our plans, he said to us there are some test we need to have them done and then we went to the hospital to run all the tests.
Then after a week the results were out and then the result for the genotype turns out that we are not genetically compatible, that is we are  (BOTH  AS) meaning we both have sickle cell trait, and now because of this my parents disapprove of the union. My parents said over their dead bodies for us to get married or to see me getting married to the guy, though they said they are okay with him but for the fact that we are both same genotype they will not allow the marriage to take place, and also because I already have a step sister who is SS in my house. 
My parents asked me to end the relationship with the guy before I leave the country but I could not do that because I still love him. But I had to let him know that my parents and every of my relations around me is against our union together but he still tells me he doesn't care. Since I left for my masters and came here we have been communicating, no day passes by without we talking to each other. He said to me he can't leave me because he doesn't know how to start dating another girl and he said to me he loves me so much that he can't let me go and hopes we get married this year December. And I also don't just have feelings for anyone at all, even when other guys keep on disturbing me, also the pastor says they can't conduct any wedding for us since we are same genotypes and advice we go our separate ways, that we are not meant to be.
Now my guy in question believes that a miracle can happen and keeps on telling me we should fast and pray for the genotype to change. Anytime we talked he always say we can do this together and that we would give birth to children and we won't have any (SS), and he said he is sure we will give birth to (AS).
Now am so confused since I came here to school, I don't know what to do. Anytime I try to share my problem with any of my friends they always tell me to please end this relationship and free the guy to go but am still into him.
The problem now is, how to tell the guy I can't marry him without hurting his feelings or him thinking I have met someone else cos presently am out of the country, am doing my masters right now.
Please How do you suggest I convey such message to him.
Thanks..

If you have a step sister who is a sickle cell patient, I'm certain that you have an idea of what crisis feels like, and the cost of taking care of a sickle cell patient. 
Though it's not advisable for anyone to take chances when it comes to a sensitive issue like blood genotype compatibility, the truth is that two AS couples can marry and not have any of their children as a sickle cell patient. 
Let me explain, the chances of getting an AA genotype children is 25%, the chances of getting an SS genotype is also 25% while the chances of getting an AS genotype children is 50%.
There's every possibility that AS  and AS couple can get married and have all their children as either AA or AS without any SS, but the truth is that there's also a 25% chances of having an SS child, and I can tell you that it's not something you wish to experience as a lady or as a parent. 
So it's always advisable for intending couples to eliminate every and any chances of getting an SS children because the pressure, emotional challenges and the stress that comes with taking care of such children is much more than what your emotions can contain. 
Though it's a difficult moment, please I will first suggest that you go for another genotype test so that you can ascertain your genotype and eliminate any human error in your first test. If your genotype is AS, please encourage him to go for another genotype test in a different hospital. If he's AS, then you may then let him know that you have decided to move on with your life because you don't wish to bring any child to this world to suffer in pains and agony that could be avoided.
There's no better way to convey your message to him than to let him know about your decision and convictions with respect to this. 
You may also encourage him to read this article and understand the reason why he shouldn't take chances if he can eliminate the possibility of having a sickle cell patient.