I think that there are different levels of "straight".
Personally, I am "hetero-flexible". I do not consider myself bi. I do not actively persue other women to have sex with. I do not mind receiving oral from another woman but will not usually give. There have been some women in my college days
that I did perform oral on willingly. I have yet to find a woman that I am attracted to enough to want to do it. Thus, my definition of "hetero-flexible".
While some people may think that just the act of being pleasured by someone of your own sex makes you bi-sexual, I do not agree. I think that it's the act of you pleasuring someone of your own sex as bi-sexuality. The difference is whether you are giving or receiving. Possibly, he too, feels the way I do.
Why are we so quick to place labels on people? Just enjoy the pleasure.
Just my $0.02
LC