Yes, a persons' orientation can change.
How to Get a Straight Guy to Like You: Can You Make a Straight Guy Gay?
Maybe you feel the same. Easier said than done, I know. Is there something that you don't like about yourself? Gay men in particularly are guilty of this. They don't need to mean anything about who he is.
If this is the case, you may want to steer clear anyway. You may not be able to form a genuine bond of friendship with this guy if you feel this way. There may be a deeper, subconscious issue involved here, but that's beyond the scope of the article. You can't make him feel for you. Anything that happens between the two of you stays between the two of you.