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Hey there,

I think that the best thing you can do is sit down with them on a day when they are in a relatively good mood. It may help if you plan out what you are going to say before you sit down with them to make sure you cover everything you want to tell them. The main points you may want to cover are the fact that you are bisexual and would like their support, and the fact that you have a girlfriend. It may help to tell them how long you two have dated. Try to anticipate any questions they may have and answer them, and make it known they can ask you things.

You also have the option of telling them through something such as a letter. This allows you to get out everything without nerves and interruptions getting in the way. I'd still tell them the above things. They still probably will want to talk to you but at least everything will be out.

Maybe you can print out information sheets or pamphlets about bisexuality so they can get a better understanding.

So, the best plan of action would be to be honest and open with them. I wish you the best of luck!

-Dez