First of all, to answer your question: are your feelings for him love. First of all it's easy to mistake that for love when you know you're dependent on him and see him as a lifesaver. Secondly even if you do love him, you have to consider whether you can marry him and whether the marriage will last, you said he doesn't have much money, so ok suppose you marry him, can he give you the life you want and an expensive wedding. You are only 18 years old, do you know what kind of life you want in the future. Do you know what kind of life you want for your future children? Are you sure that if you do get married to him that your depression won't come back when you realize that you can't live a happy life after you get married to the person you like.
Secondly to talk about the problem of depression, depressed people first go to see a psychiatrist, so that the psychiatrist to determine whether you need to take medication, and secondly, if there is a knot in the psyche of the words while doing psychological counseling while taking medication, itself, people in the fragile time it is easy to rely on other people, if you go to see a psychiatrist when you meet a doctor who takes good care of you, you will not fall in love with or rely on that doctor again. If you go to a psychiatrist and meet a doctor who takes good care of you, will you fall in love or depend on that doctor again? So for adolescent girls, like or love or dependence is a very normal feeling. You should not magnify this feeling too much. After all, you are still young, and you will meet and like a lot of people in the future. You still have a lot of books to read, a lot of knowledge to learn, a lot of road to walk, and he, even if married to you, can not accompany you to walk too much road.
Finally, let's discuss why he hasn't done that with you. I don't understand why he is 50+ and still not married, and I have to tell you something that you may not be able to bear, some guys (not for any guy) don't get married because they are of average financial ability and don't want to bear the burden of a family, some guys don't get married because they don't want to be responsible for a girl, and some because they want to live their life in style without any pressure of any kind. If he said to you later to give you the future of the marriage of such words, if he is not joking, it shows that the man he does not want to take responsibility for the family, or he felt that he did not have the confidence to take responsibility for the family, he did not have the confidence to be responsible for you, this lack of confidence may be due to the age difference between you is too large, it may be due to the two of you are not too good economic ability, but also because of his family of origin, it may be due to his family of origin. This lack of confidence may be due to the age difference between you, or it may be due to the fact that both of you are not too well off financially, or it may be due to his family of origin. I think it's up to you to figure out the reasons. You can observe by yourself or ask him directly, but once he says he doesn't want to marry you or something like that, I hope you can accept this and continue to get along with him.