Really it comes down to values and compromise, although it may seem best just to be upfront and honest with your feelings (in most cases it is...), in this situation, will it hurt and damage other things you don't necessarily want them to?

Like what if he doesn't like you? Then he thinks you're trying to take him away from his girlfriend. Really not such a great idea.

However, on the flip side, just being honest about it does confront the issue and bring it up to face, and if you're worried about the potential girlfriend issue after he has expressed an interest in you, talk to him about it. Problem solve, because we don't want someone unecessarily hurt due to the drama of relationships, and emotions.

Best of luck

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'Let "desire" be forever stricken from the dictionary, and
from the soul! I retreat before the dizzying farce of
tomorrows. And if I still cling to a few hopes, I have lost
forever the faculty of hoping.' - E.M Cioran

So go for it.