Hi there, It's a very difficult thing to come out to somebody. And very brave. I hope you'll take my advice with a pinch of salt because I'm probably not the best person to answer this, but I might make you consider a couple of things. First- if you have a friendship with your straight crush and you come out to them, it is important you understand that they may feel differently about you. This may be because of homophobia- but it could also be something else. When you're friends with someone there's an implicit trust between you. Part of having a platonic friendship with someone is the trust and agreement that it is not a sexual or romantic thing. It can be very difficult for that person to understand you if you come out and tell them you like them at the same time. The reason being is because in their head, they may think that you only got close to them for sexual reasons, and not for friendship and companionship. This can happen with straight friends too, it isn't anything to do with sexual orientation. So because of that, I would be careful about how you discuss this with your friend. Assure them that your attraction to them isn't the reason you are friends. Assure them you can get over it if they aren't interested. Let them ask questions. If it is someone who truly cares about you as a friend, they will listen and understand as best they can. If they have a negative reaction, just know that not everybody would and there are other people out there who are far more accepting. I wish you the very best of luck. I've included a link below to a group on here that may be better suited to answer your question and give you some more experienced advice than I would have.
Sexuality Questions Group on BlahTherapy 
