Good evening, I would like to work to assist you with your question.
I think that if your stepson is repeating that he loves you and his father and he never wants to loose you, and that's not something he typically does, I would not assume that it is normal; however we must consider his age. He is 7, and at this point in a child's development, they are beginning to understand a lot more about life, as well as death; so maybe in some way he may be thinking about this. Have you or his father questioned why he said he doesn't want to loose you?
meaning have you asked him?
I would first suggest that if you haven't already, that you and his father ask him why he said that he didn't want to loose you. Is it something that he's seen? Heard about? Why is that a concern for him. Secondly, if your husband has a respectable relationship with your step son's mother, I would suggest that he make her aware of what he is saying, and ask her if there is any particular reason that he may be saying this; perhaps she has heard the same thing. Your stepson also, knowing that his mom is engaged may be fearing the idea of a new man stepping in the position as a father, or he may even feel as though he is loosing his mother to her fiancee. This is why I say that it would help if his father has a good enough relationship with his mother to talk to her about these things concerning your stepson.
This way, if there is anything that his mother can do on her end to ease his fears of losing you and his father in some way that would be a big help. Another thought is that your stepson may have enjoyed being with you and his father for the two weeks, that he's having a hard time readjusting to life back at his mom's. If this is the case, see if your husband can talk to her about keeping him for longer periods more often. Maybe being around you and his father more often will help him to see your permanence in his life.