Sexual identity

I'm 26 and have always thought of myself as being straight and never questioned it. I've always constantly been very turned on by girls in real life situations since I was about 9 and consider myself to be more red blooded than most guys I know. I get erections in public places by just looking at an attractive girl.  The problem is that I've been using porn for years now and decided I would check to see if I was aroused by gay porn. I've checked before and have been aroused but this time I was intensely turned on, more so than I can ever remember and could have ejaculated without touching myself. Btw, it was a solo video of a muscular guy with erection. I have thought about it since and again I have become intensely aroused. I makes me feel really bad and filled with anxiety and I pray not to become aroused which I believe heightens it.
Also, I have read that plenty of straight guys become aroused by gay porn and the sexual act but this was solo and it is the fact I became probably more aroused than ever that really gets to me.

This has now made me question my sexuality which as I say I have never done before. I have always been in relationships with  woman (though I've only been in love once at 16) and as I say constantly desire woman I see day to day wishing I could sleep with them. I really love the female figure and I love being around woman and picture myself settling down with a woman once I find the right one. I have never in a real life situation been attracted to a guy whatsoever, could never picture myself kissing a guy and could never picture myself settling down with one.

Which brings me to my question. Based on what I have said do you think my intense arousal is just down to a porn addiction and a quest for novelty or could this be a sign that I'm at least bi-sexual? It makes me wonder because you hear of people 'realising' later in life.
Your reply would be much appreciated as this is really mentally effecting me and I need some closure on it.