No. Just because a man does not want to go out with you, or continue going out with you, does make mean that he is gay.
Maybe, just maybe, he does not want to go out with you because you are not an appropriate match for each other.
Or perhaps, you weigh 300 lbs., and are in complete denial of this fact. Maybe you wear tight clothes to go with your "full figure." And, when you have difficulties getting pregnant, you will blame everything, except your state of obesity.
Or maybe, you are very loud, and have to stick your nose into everybody's business, and make sure that everyone has the benefit of hearing YOUR opinion.
Or perhaps, you have just been brainwashed to think such idiocy by your "rebbetzin" at "sem."
But, I guess "blaming the guy" is always the best course of action, so that you don't have to face your own middot you desperately need to work on.
If you have to accuse the guy of being gay, just because he is not in the least bit attracted to you, physically, emotionally, spiritually or any other way, then that must mean that you can't accuse him of being poor, stupid, unsuccessful, or unattractive himself.
In other words, he's a real catch who you just can't have.
Calling him "gay" is just the shidduch world's form of sour grapes.