Thanks for your question.
There are several ways to tell him bisexuality is a part of you. First, you can be clear and direct with your boyfriend and say something to him like this:” I know it is not something familiar to you, but I like girls and boys and I want you to accept it as a part of me”. This way he will understand he must deal with your sexual orientation and has to accept who you are.
Maybe the problem is that he doesn’t exactly know what bisexualty means and the solution is to informs him to break his prejudices about this.
The third possibility is your boyfriend is maybe jealous, insecure or afraid that you can fall in love and leave him for a girl. If it’s the case, just reassure him that you sincerely love him.
Thank you and good luck,
Sabrina for AlterHeros.