In addition to having sex with you on an almost daily basis, he masturbates a lot, most likely fantasizing about other women while doing so. Why you worry is the main problem here because being gay isn't a problem. Most men (and many women) masturbate even when they are in a healthy and sexually active relationship. If it's against your beliefs or something like that then i can see why you worry, but you say you have never had any problems with gay people so you must not have any strong beliefs that people must and should be straight.
All these sexual orientations are perfectly normal. Using this perspective, you can figure out the answer for yourself. While masturbation among two or more men is clearly something likely to happen if a man is homosexual, it's interesting to note that many heterosexual men have also masturbated with another guy. One has to keep in mind that these online quizzes are not answered generating algorithms and codes, but it leaves you with certain thoughts to ponder.
