Blindsided

I think you have it right silver. And MHHHD2 I think the bit from shoreline onwards continues this theme- that it is the end of his relationship etc.
And the main line “Cause blinded I am blindsided”, means to me that by ‘her’ he was blinded... and therefore blindsided- seeing only half of the situation as she was hiding, or he was kind of hiding from himself, the truth. Bike down... down to the downtown Down to the lockdown... boards, nails lie around- Pretty obvious. He’s just setting the scene(biking down to where she is... possibly in what sounds like a shed with someone else.

I crouch like a crow- Showing us that he is being sneaky/ not meant to be seen. Contrasting the snow

For the agony, I'd rather know — For even though it may be painful, I have to know the truth. The first 2 verses are basically just describing the setting and that he’s “not really like this” (someone who spies and is suspicious). “I cup the window crippled and slow”- Just his movement; he cups the window (i.e. peering into the window through the cup he makes in his hands. Slow in movement cause he’s sneaking. For again, even though it maybe agonising, he wants to know the truth.)

And “would you really rush out for me now?” could be him saying if she (whoever ‘she’ is) saw him looking through the window, catching her in the act, would she care enough to rush out to him. -“I’m probably plight less.” Without promise or betrothal (engagement or promised to one another. This shown through her actions of cheating on him- she hasn’t kept her/a promise to him i.e. to not cheat) -“Taught line... down to the shoreline The end of a blood line... the moon is a cold light”. Here he is again setting the scene (For me I see him just walking in thought to the shoreline.) whilst basically saying it’s the end of his blood line for he has lost his love- the woman who would have had his children thus continuing his “bloodline”. And also the moon being described as a “cold light”; I think this could mean it is a harsh reality, as its shares “light” on his situation i.e. uncovers and exposes truths. It is cold and painful.