Of course it doesn't make you gay. It is just a masturbation technique, you're not getting a penis inserted so there's is nothing gay about it. If your girlfriend is up to it, she can be the one in charge. Some girls like the power play of it.
Just a word of warning, my freind Jon got fingered up the arse whilst been blown by a girl, he lost wood almost immediately and has never been the same since. Not gay or anything, he just can't look anyone in the eye anymore and has an overwelming feeling of guilt all the time.