Chad thanks for your question,
Many gay teens, who are still in the closet sometimes experience the situations you have described in your question. There are many factors involved in the coming out process; including personal acceptance, surroundings (family, friends, peers), cultural/religious beliefs, local law/society and the situation that a person questioning their sexual orientation is living in. You can read more about coming out issues here https://alterheros.com/english/dossier/ViewCategory.cfm?ss=j&CatID=2
Many elements that you have stated in your question are perfectly normal and happen frequently to teens during the period of sexual maturation and discovery of orientation; In most cases for boys the period is between the ages of 11 to 17 or sometimes older in the case of affirming orientation or sexual identity. Younger teen and pre-teen boys often compare and look at each other, mostly because of curiosity; another reason is that male genitalia is apparent outside of the body, young teens get uncontrolled and embarrassing erections that just increase their curiosity. This curiosity also exists in girls but usually happens in the mid-teenage years as hormone levels spike, the genitals enlarge and pubic hair grows. Your question however is beyond curiosity; it has to do with fantasizing, sexual desires and sexual attraction.
Even if parents and many adults are not aware; many teens partake in sexual experimentation, regardless of their sexual orientation, these include the elements mentioned in your question:
Visual: Looking at pictures or video, talking or texting in a sexual manner, undressing, comparing genitalia, looking at someone with or without their knowledge (Voyeurism), smelling, touching or wearing clothes/sports gear (Fetish or fantasy)
Physical contact: Touching, slapping, wrestling, massage, fondling, using objects, sexual games, kissing, oral sex, intercourse.
In the case of arousal or fantasizing of a sibling; proximity is one important factor in the unhealthy lust and/or sexual attraction towards a sibling or cousin or other family member. Because you spend a large amount of time in the same location, or living under the same roof with the person, the proximity and convenience factors become apparent; especially if you live in a community that has a small population of people your age and/or the area you live in is isolated, requires a car to go towards a more populated town or a city where other teens would hang out. Places like coffee shops, clothing stores, community centers, malls, sport facilities, parks and so on. Another factor is that you have an established relationship with this person, you know them very well, it’s a familiarity that is comforting; here, he is your brother, the friendship is there already. Meeting new people and creating new bonds takes work and effort, especially in the case of a gay or bi or questioning teen. Another factor is sexual tension and the need for sexual outlets; looking at pictures/videos online and masturbating is sometimes not enough of a sexual outlet, you have a need to see and feel a real person.
Having sexual relations with a sibling is considered as inbreeding and is called incest. In heterosexuals, it is a threat to human life (lack of biodiversity in the genetic pool). Incest is illegal in countries around the world. In male-to-male sexual activity there is no risk of reproduction, but their still exists a risk of sexually transmitted infections (when not wearing a condom), these also include external aggressors that condoms do not protect against like Crabs (pubic lice) and Scabies (parasitic mites).
Also, in the case of an older teen or young adult, a sexual activity is wrong if it is between an adult and a young teen who may not have enough sexual maturity to consent, this sexual activity has been deemed illegal and is considered rape, sexual abuse or sexual interference under US & Canadian laws.
To answer your question about telling your brother or acting on these feelings, you must judge carefully the situation, it is likely that your brother may act negatively to this, especially if he is older and has established his heterosexuality; is interested in girls or is dating or has a stable girlfriend.
It is better to have your brother on your side, don’t shock or put him on the defensive, be honest with him that you might be gay, and that you need his help to get you information on local GLBT youth support groups or gay/lesbian resources that may exist close to your town or in an adjacent larger urban center. An older teenaged or adult sibling can be a valuable person you can count on in difficult times, he may be able to help you when you are ready to come out to one, or both of your parents, or the rest of your family.
In your second question you ask about how to meet other gay guys, here is an article that was written on the topic
Another question I answered how to tell if could also be of help, even if it was written concerning females, the way of determining if someone is gay is about the same. https://alterheros.com/english/ask_experts/ask.cfm?QID=1686
I don’t know what area you live in, but if you live in Canada or the US there are support group in most major cities and phone support in some provinces and states. Use the Internet to try and find a local GLBT group in your area. If not, get in contact with a HIV/Aids organization or a youth health clinic or a large youth community center: they often have knowledge and contacts with groups that offer support that may not be published. At your school their may be a school nurse or teacher you trust enough, who could guide you towards these resources as well. In Canada you have the right to seek medical and mental health resources on your own starting at 14 years of age without parental consent. However parents do have access to your medical record and a hospital or government health agency may contact them if you are under 18. So look for services that are free and confidential.
www.thetrevorproject.org in the US
www.youthline.ca/about_us.php in Ontario
www.caeoquebec.org/gay-line.html in Quebec
JP volunteer for Project 10 Montreal.