Homosexuality isn't just about having sex with a member of the same sex. It's more complex than that. There are three main factors that measure gayness: Dominance/submissiveness, masculinity/femininity, and the number of dicks and dick-like objects involved.
The straightest form of sex is between two feminine women. The gayest form of sex is between two masculine men. Sex between a woman and a man is somewhere in the middle. Sex between a tomboy and a feminine women is gayer than sex between two feminine women but straighter than sex between a man and a woman. Sex between a man and a trap is gayer than sex between a man and a woman but straighter than sex between two masculine men.
When it comes to individual sexual acts its participants and measuring their gayness, you have to take into account their dominance/submissiveness.
A man being pegged by a woman is straighter than a man being fucked by another man. But is the man being pegged straighter than the man who is fucking another man? Probably not. Because that man is dominant while this man is submissive. No matter how many men you fuck, as long as you've never been fucked by another men, you can't really be considered gay. The same goes for oral sex - a man orally pleasuring another man is gayer than a man orally pleasuring a woman, but the man orally pleasuring a woman is undoubtedly gayer than the man being orally pleasured by another man. It's even arguable that a man being submissive to a woman is gayer than a man being submissive to another man.
When it comes to women, a woman fucking another woman with a strapon is gayer than two women tribbing, since that involves imitating a sexual act that involves penises. When it comes to threesomes/orgies, obviously the more men/penises involved the gayer the act is, etc.
Overall, the issue of gayness is a pretty complex one and not something that could be properly explained in a single 2000 characters 4chan post.