He apologized after sexting

I have been talking to this guy long distance for approximately a month and we have gone on one date, which went extremely well. Between our first and second date there was a day when the conversation turned sexual and he sent me videos of himself in the shower, and pleasuring himself. I’m attracted to him so I played into it a bit and shared a nude. But afterwards he apologized for being inappropriate with me, yet admitted he kept the nude photo. Why would a guy do this? Get super hot and heavy then pull back and apologize??