It always has to do with distance. How close something is to you, usually increases the chances of you wanting to reach for it. If you are married to a non-believer, you are not going to convert her... you are going to be converted. If you put an orange next to you while you're watching TV, you'll most likely reach for the orange at some point. Not counting factors like boredom, loneliness and depression, urges themselves usually occur under these conditions:
- The first reason (if you have just relapsed) is because you have just relapsed and your body is still craving that recent rush it just received... And there is no such thing as a "satisfiable sexual craving". That craving will NEVER be satisfied no matter how many times you orgasm. Remember that it's almost always about distance not the urge itself. Your flesh knows that porn is close by and therefore it wants it here.
- The second reason is because porn is close by and therefore your flesh wants it here. It sounds just like the first one because it is. All urges are. Again, if you're still watching things that stimulate you sexually (even a just little bit) you remain in that constant state of "activation". "Today I didn't fap or watch porn, I only stared at a woman's body at the grocery store, watched a video of a woman dancing seductively and listened to sexual jokes on a podcast... so why am I still having urges?"
Honestly when it comes to this subject I don't mind repeating myself at all. I don't have the strength to condemn anyone because I was in that same boat, and I'm still learning these things the hard way. The way to properly do Nofap is to cut out anything sexual from your life because it will eventually cause you to stumble. Don't confuse this with having sex with your wife, which is a command from God, not lust. But if a video even hints that there's going to be sexual themes, you have to end it and move on. Yes, be paranoid. If a woman is dressed in a way that is clearly designed to turn you on, look away, mind your business, and if you have looked, don't take a second look.
If you ignore this and continue to watch content that is mildly tempting, with the thinking that: "At least it's not porn, and anyway I should be allowed to watch anything if I'm really healed" then you are delaying the healing. And I only say this because I was delaying my own healing for years because of the things I was still engaging with.
It's very rare for urges to occur in a vaccum. Temptation of all kinds comes under specific conditions. The devil had to wait until our Lord Jesus Christ was hungry and alone in the wilderness in order to tempt him. And the first thing Jesus Christ did was use scripture to put distance between Himself and sin.