I think you are asking the wrong question. I don’t know if he is depressed. But I do wonder if he is the man for you. From your letter, it sounds like this man barely knows you but is offering marriage. Although he states he loves you, he also indicates he is hurrying to marry because he thinks he missed meeting the right person while in college. That isn’t a very compelling basis for making a lifelong commitment.
Also of concern is how different you are. I don’t know if he is clinically depressed but he certainly doesn’t sound very happy or very involved with life. You, on the other hand, have many interests and like to be with people. Imagine what it will be like to be married to him. Will he be content to stay at home while you go off to do things with friends? Will you like doing things by yourself? Or do you think you will have to adapt to his lifestyle and give up all the things you like to do to be married to him?
If you are seriously considering marrying this man, I hope you will find a way to spend some extended time with him to see what it’s like to be a couple. If you can’t do that, I hope you will talk deeply and seriously about his expectations and yours for what it means to be a married couple. Are you compatible enough?
You are young. You have plenty of time to find someone else if the two of you aren’t a match. Both of you deserve to have a happy life with a partner who really wants to be with you.
I wish you well.