dad using my panties


im a girl who is 13 years old, and lives with my dad. a few weeks ago i had an early day at school. when i got home early, i passed by the laundry room and saw my dad masturbating with a pair of my panties. his penis was big, he was rubbing it, and i saw him shoot his stuff a couple of times right on my panties. i was so shocked, that all i did was say ewwww, and went to my room. a few mintues later dad knocked on my door, said he was sorry, and that my panties were going in the wash anyway. i didnt answer him. i text my friend and told her about it, and she said she saw her brother do the same thing with a pair of her panties. another girl told me she gave her boyfriend a pair to use, also. is this a guy thing ? should i worry about my dad doing this ? havent talked to him about it, or much of anything since that day. any advice ?