Depends how we look at it. One could say 4, which isn't false, however isn't true either.
What we know about human sexuality so far can be shown on a triangle. The top of it represents the Kinsey Scale, the bottom tip asexuality. Considering the number of points on the triangle is infinite, there is an infinite number of sexual orientations. In case someone doesn't understand what I mean, here's a picture:
A person may be placed anywhere in there as they can be homoromantic asexual or homosexual heteroromantic, demisexual etc. The differences between two points may be subtle, but will exist.
Of course, this doesn't include autosexuality or pansexuality, however personally I'm doubtful of their existence as a sexual orientation and leaning more towards it being disorders or variations of something on this triangle. This is, however my personal opinion and I'm not a specialist.