I’ve come across several answers to this question in the internet. Although there is disagreement on the timing, almost everyone said that he has to tell his girlfriend if he’s a bisexual. Why so?
Personally, I think there is no need to tell. Reason? Because there is no reason why he ought to tell, is there? Ok, let’s put it this way. Does a straight man with a girlfriend tell that he is straight? Then why demand the same from a bi?
The only reason why a girl would like a bisexual man to tell her he is bi because she wants to know if he is capable of falling for another guy, and leave her for him. Falling in love with another person is not limited to bisexuals; straight and gay people do as well. But girls never expect straight men to be upfront and say that he is capable of falling in love with other girls.
What girls should be asking all men, whether straight or bi, is whether they can commit to a relationship and be faithful. Ask your man how he is going to handle it if he falls for another person while still in a relationship with you. Ask a man, straight or bi, whether he would value your relationship more than whomever he falls in love with in the future, and avoid any sexual relationships with another person. If he would prefer growing old with you. And ask this question if he is your boyfriend already, which means he already passed a lot of your tests or ticks most of your criteria, and you do have a relationship. And ask it during your most romantic moments: a valentine’s date, an anniversary date, or any moment when both of you are really feeling romantic. Make sure that before popping this question, he really feels romantic to you. Then you can periodically remind him about it. Provided you take care of his needs, I don’t see why he wouldn’t reciprocate, even if he’s bisexual.
What if a bisexual man turns out to be unfaithful? Well, how would you treat an unfaithful straight man? Do you completely cut off the relationship, give him another chance, or join in? The same rules apply.
What if a girl would like to know if he is bi because she wants a manly man? Well, you don’t have to ask that. Reject him outright if he doesn’t seem like a manly man to you. But just keep in mind that some manly men are gay men, and some not so manly men are straight men.
What if a girl wants to know only to make sure that he desires him really physically? That he is at the very least not gay, pretending to be straight or bi? Common girls, this shouldn’t be ask, you know what to do. Although him making love with you proves that he desires you, a man sleeping with you does not guarantee that he is in love with you. He could just be a jerk who wants fool you. You have to look for other’s advice on how to test for love. But then again, if you just like a fling, a one night stand, a shallow relationship, a short time relationship, a relationship based on lust, someone to scratch your itch, or just to taste him, a friend with benefits, a part time lover, then no need for questions. Hop right in. You’re an adult, no need to be reminded of the consequences. Don’t come back crying.
What if you discover later on that he is bi (he voluntarily revealed himself to you) or worse gay? Provided he has not been unfaithful, ask the same questions again. The same questions that you should be asking any man: Does he desires you in a sexual way? Is he capable of being faithful to you? Does he look forward to growing old with you? Is he going to conduct himself decently about his sexuality (for a straight guy, this means not sleeping with another girl)? Is he not going to bring shame to you? You know what other questions to ask. And if his answers please you, why not give a bi man a chance.

