Yeah, as someone else has said. I can only suggest subtly expressing your sexual preferences- whether it is talking about a specific celebrity your into /passerby and if he acts confused or laughs like he doesn't take it seriously, be like "I am bi, you know that right?". Very subtle and casual rather than a 'coming out' type of situation with your mate, which I am sure you are probably not wanting to make a whole label of everything and emphasise your sexuality in a small conversation. You know what I mean? Randomly letting him know your bi, mid conversation could be nerve wracking and awkward. I think its old school having to let your friends know your sexuality in such a formal way in case they, i don't know, aren't into it or end up not liking you anymore (ugh). Best to be natural and informal because this is who you are and there is no need to label yourself to him because at the end of the day, he is a friend.
Casually make your preferences apparent and see where the conversation leads! In this way, if he is a good straight friend, you've got a great person in your circle! Or if he is on the spectrum... give it some time now that both of you are open! No need to jump in and get excited, this is your chance to maybe start flirting or making your attraction apparent. Whether it is a straight crush or a crush with someone on the spectrum, a good amount of time is always best to really be sure that you don't just reeaally get along with your friend and THINK you have a crush on them or if you yourself are genuine with your feelings. Trust me, I thought I liked a good friend of mine, but once we started talking for a while in a romantic environment after confessing- eeek! Just turns out we just get along well... but was not feeling it romantically.
1. Make your sexuality known
2. Find out his opinion/his sexual preference
3. If he is straight- no worries! You still have a great friend
/ If he is on the spectrum - leave it at that (for now)
4. Following the latter point, make your attraction known, build up your affection or flirting
5. Confess when you feel right! It is always great to let your feelings out- but be prepared, confessing to friends can be hard !