There are a few thinks a man does that are sure signs he sees you as more than a girlfriend for now. It's all in the way he treats you. He has to see you as valuable and he has to feel to the core of his being that losing you would be a huge mistake.
If your guy watches out for your well being, that is a sing he is thinking marriage. By this I mean does he do things to help you out. An example, say your brakes or tires are bad on your car. If your guy goes the extra mile to make sure you get this taken care of, you are more than just a girlfriend, he really cares about your well being. If he just casually suggests you get it fixed, well, he may not be as invested as you would like.
If you get sick or are under the weather and he shows you with actions that he cares and doesn't just vanish until you are better. He goes to the drug store to get you something, or he brings over food or just wants to be with you regardless of your mental or physical state. If he sticks around during your worst days, he is marriage material and it just may be you.
If he always spends most of his weekend with you and makes sure you are included, he sees you as commitment material. A guy who wants you around more than not is into you. He has potential to commitment and is marriage material.
When your guy starts making future plans with you, this is a sure sign he is thinking long term. If he plans vacations and trips months away and your are a part of it, he sees you in his life and he could be thinking marriage. If he asks you to attend weddings with him, this is a sure sign he does not fear commitment.
These things mentioned above are signs he is into you and thinks of you as more than just a girlfriend. If you feel at peace and secure in your relationship even when you are a part, that is your gut talking. Your gut is usually very accurate. If you feel this way, chances are you are correct and he is thinking marriage.