I'm applying for my U.?
It might, but not in a good way. You see, the consular officials are always looking for people who might be tempted to overstay their visas (or maybe never leave at all), so if they think you have an American boyfriend then that would NOT be a point in your favor, because its a potential reason why you might decide not to leave on time. It would be better if you just said you wanted to go sightseeing and maybe visit some friends, which after all is perfectly true. The US government is one of the most annoying institutions on earth, and generally speaking its best not to volunteer any information youre not specifically asked.