The flowers are wrong for C angustifolium. One of the many Epilobiums. A sense of scale would be helpful.

This is the only other photo I have. The plants are about as tall as (or slightly shorter than) swamp milkweed.

I've never seen swamp milkweed. Can you estimate the height?

its definitely not C angustifolium, though.

Hard to be sure but I would say these were about 3 to 3 1/2 feet tall.

Epilobium ciliatum fits your description. The flowers would be pretty small - a quarter inch or so across. If I remember right there are some others that look similar that are about that size too, but you need a technical manual to key them out.