Your friend needs strong, supportive, positive people around them to help deal with prejudice if it arises. If you then don't have the conviction that being gay is natural and good, you may want to reconsider the friendship.
Practice love and tolerance of all people of any lifestyle. The Normal Heart (2014 TV Movie) A gay activist attempts to raise H.I.V. Read literature from both sides of the debate, especially those with a religious background, and pray and meditate. Shelter (II) (2007) When his college dreams are sidelined by family obligations, a young man finds comfort in surfing with his best friend's brother. A religious leader can explain the position of your faith on the matter.
If you do not think that you can provide the person with the same quality of friendship, then it may be better for you to end the friendship. If you are really bothered by your friend's sexual orientation, then you may need to think about whether or not you can still be a good friend to this person. Decide whether you can continue the friendship.