Influx:
OP, sounds like you're pushing yourself too hard to identify as straight, tbh. If you find male wg to be erotic and then say you have great sex with your wife as result, there's a good chance you're leaning more towards the bisexual space.
Your attraction to men seems to be solely on fat men, which is fine - that's a preference, everyone has physical preferences. But I'd seriously reconsider your reliance on thinking you're straight. You experience attraction to select male attributes.
Bisexual doesn't mean attracted to everyone, all the time. Seems to me you have limited attraction to men, based on weight. But you lean more towards women generally.
Anyways, just a suggestion to look deeper into your feelings, and learn more about yourself. I just feel you're overcompensating to adhere to the straight label, considering you put it both in the title and it's the first thing you said in your post.
I don't know about this, I could apply the same logic to any time a man watches porn that has another man on-screen. Sometimes there's just a vicarious thrill, and that's enough. No need to needlessly speculate on someone else's sexuality.