My advice to you is to simply be comfortable with who you are. There is no reason to have to bend or modify yourself to fit within the standards that others have, even if it is your mom. So your mom doesn't believe in bisexuality, or thinks it's a phase. Indirectly she's actually pushing you down a path that involves experimentation to clarify your sexuality. Instead of supporting you and helping you discover yourself, she is placing you in a situation where you might take risks to experiment or you might mentally suffer trying to fit into her expectations of being gay OR straight.

Although it's not exactly the same, I think that my experience in coming out might provide some insights. I'm rather old, 45+ male, and I've known since I was a teen that I am gay. At one point in my life, I met a woman and although I wasn't directly interested in a physical relationship, I quickly grew to love her and developed an attraction to her. The thing is for years I acted straight because it was the thing to do when you are in a monogamous heterosexual marriage, with children. Internally and in our relationship I accepted the label of bisexual because it was more convenient, and meant I didn't have to argue to justify my true sexuality.

I was not that long ago that I finally came out to my family and friends...yes that even means coming out to my wife. Not that anything in my life changed, but for mental health reasons I had bring the internal conflict to the surface. So I came out as "gay", even while I am still in that monogamous heterosexual marriage, with children. Did that work out easy? Not completely...I've explained my feelings and logic, and stated that I respect that others may not agree with my label. However, being a "gay man married to a woman" is WHO I am...and it's who I am comfortable being. Others don't have to believe me or agree with me...because if I am not comfortable or happy as me...well nothing else matters.

So, back to my advice. Be comfortable with who you are...not who others want you to be. You don't have to go out and experiment to prove yourself to someone else. Believe me, I've been told "you can't be gay if you are married to a woman"! I'm not going to go out and have gay sex with 100 men to prove I'm gay, and you don't even have to "get some experience with both guys and girls" to prove you are bisexual. If you feel bisexual, then you ARE bisexual.