I need a bit of help and/or opinions

I was staying around my mates house who ive known for about ten years, hes about 2 years younger than me and we're best friends, whenever i sleep round his house we have discussions about everything. A few times we had a discussion about havin gay sex and it not meaning your gay. Now im happy with my girlfriend and everything but i was watching a porno vid with him about a month back and i suddenly had the urge to grab his dick, i dont know why. gay sex cant be all that bad but i got put off when he changed his mind saying he doesnt really know whether he'd like to have gay sex. I dont know whether to approach him about it or not as i do not want to ruin our relationship so wot do u guys think i should do.