What Causes Tear On Penis Head And Redness Of Penis Head During Erection?

i see a very slight tear mark at the corner of opening/tip of my penis. whenever it get erect the whole tip are becomes so red as if its going to bleed. the erection are not at all hard as it used to be. this happened after i masturbated once when i was drunk and i don't know what i did with my penis. can you please help?