Questioning gender identity.

I'm posting here bc I really don't know where else to get advise. Rencently my best guy friend and someone that I've dated and had a sexual relationship with (we aren't together now bc of other circumstances but we continue to be more than friends) he confided in me that he's questioned his gender identity since high school. I'm a very open minded person and I love him no matter what, that's not an issue. I just don't know how to help him. He isn't sure how he feels about it. I guess I just want some advice on how to help or talk to him without our personal relationship impacting it. I want him to do what is right for him. Any help would be much appreciated just no hate comments or saying anything mean about him. Thank you!