HOO BOY! Thats alot to think about. You have to ask yourself though, are you ready for any of this? Like this guy, is 28 a big age difference, because if you are not 18, this is classified as sexual assault, unless you have the consent of your PARENTS or something like that. Also, you should NEVER let him hit you or hurt you in any way!
As for your girlfriend, I gotta say that unless you are romantically attracted to her (would rather marry her than a man) you are NOT gay. We are sexual beings. We can get attracted to the same sex, simply because sex is involved! But if this is just simple curiosity, and you would rather choose the boyfriend of your dreams over her, YOU ARE NOT GAY, just sexually curious, and most likely bisexual (you enjoyed the sex with her and this guy, right?)
Most importantly, STAY SAFE. Always use protection.
MOST MOST IMPORTANTLY: I'm sorry, but you have to tell your parents about this guy. It seems to me that he doesn't treat you well, and your relationship with him is just for the sex. NEVER stay with anyone who only wants you in this way. You need to have a meaningful relationship with anyone BEFORE you BOTH decide to take the next step (to sex), or pain and heartache will be the only result.
PM if you need someone to talk to.