I think the problem with most of you guys is that you're trying to imitate porn.
What I mean is KEEP IT INSIDE THE BED! (inside the bedsheets)
People having secks on the bed without going inside the bed just like in porn but remember that they do it like that in porn because they gotta film it! doesn't mean that's the way it's supposed to be done.
You need to give yourself a little privacy and "imagination." Yes I know it's impossible not to see each other naked during secks but there's a big difference in being inside the bed with a woman and being outside and seeing her belly or stretchmarks every second during secks! (yuck!)
It's a sure fire way to lose an erection seeing the "imperfections" of a woman nonstop if you two are naked outside the bed sheets rather than inside. You will last longer by keeping her inside the bedsheets and seeing nothing but her boobs