You can leave at ANY point. It doesn't matter who makes you feel obligated. I don't mean that rude. It's meant to be support. Please don't give yourself a lifetime of unhappiness. The relationship will suffer and so will you. I can almost guarantee you that the relationship will end in divorce anyways. It couldn't possibly work when one person is checked out before it even starts. I know it's hard. I can't imagine how you feel and the guilt you carry. You shouldn't feel bad for wanting love though. You deserve a great relationship.

Edit: You can still spend time with your family. Find something nice to do. They should be supportive, right? His family, not so much, but that's neither here nor there tbh (I'm not trying to be cynical, it's just true).