I moved in with my boyfriend and his grandma. Before I moved in we had talked about marriage, so I assumed that we would marry shortly after I moved in. After a few months my boyfriend said to me, "You know, we are like husband and wife, even though we aren't legally marriage." He told me that his grandmother doesn't want us to get marriage, that we will have to wait until after she dies because she doesn't trust that if he dies before me that I would take care of her. Also he was married three times before, so she doesn't really trust anyone else. What should I do? Will God hold this against me when I die? I do believe in God and Jesus as my Savior.
While you talk of belief in Jesus, your belief doesn't reach the point of doing what Jesus said. "But why do you call Me 'Lord, Lord,' and do not do the things which I say?" (Luke 6:46).
You are with a guy who has been married three times. That alone should have had the warning flags raised. With that many failed marriages, I doubt that they all ended because his wives died or committed adultery. More likely he has been the cause of the break ups. I would not be at all surprised if you later tell me that he never really divorced his last wife.
Second, you compromised your morals. You knew moving in with him was wrong, but you did it anyway under the false pretense that he would marry you shortly. If he was going to marry you shortly, then you should have waited for the wedding.
Third, none of you know when grandma is going to die. This is merely a delaying tactic. If she is worried about being cared for, then why are you there in the first place? The argument is empty. A person unmarried has no commitment to the spouses relatives. If he dies before you, grandma would still be uncared for. I would be more concerned about a grandmother who encourages her grandson to continue his adultery because she sees it as a benefit to herself.
He is not a good man, nor will he make a good husband. Move out and then find a good Christian to marry.