It is believed that no one is born gay or straight. Everyone is born bisexual. Certain patterns in your life may feed one of those sides.
Now, what happened with you, may just be a one off incident or it could fuel your passion for sex with other males. Sexual orientation is a complex phenomenon. Some people are exclusively gay, some are exclusively heterosexual and a lot of us fall somewhere in between.
Surprisingly, men are more worried about being gay then women. It is fairly acceptable for a female to go through a phase in which she fancies other attractive women. There also appears to be a growing feeling among many younger people of both genders that sex is there to be enjoyed in various forms, and that they do not really want to be categorised as being heterosexual, bisexual, lesbian or gay.
You are 23 and said that your friend is much younger than you. He may have the same doubts as you. Would you know if this was his first time? You penetrated his anus with your penis. Was it not painful for both of you? Or did he take the pain easily? You are one of a large number of men who have been brought up believing that there is a stigma attached to being homosexual and fell very distressed about your doubts about your sexuality. This is natural.
Have you had gay fantasies before this incident? Are you comfortable in the presence of girls. Your Profile says that you would like to have sex? With whom?
A psychologist says that masturbation is a useful test for determining sexual orientation. He said gay people fantasize about their own gender when they masturbate whereas heterosexual people do not. So, what is it with you?
Have you fucked a girl before? If not, this act of sex with another male, is just an indication that you want to have sex at any cost – either with a male or female. The point is whether you are looking forward to another gay encounter?
My really worry is that such unplanned episodes can lead to real trouble in the form of HIV and STDs. I am sure you must have not used a condom.
It is not a shame to accept that you could be a homosexual. No point in getting stressed about it.