Am I wrong?

So I'm bisexual and have a girlfriend. We are both 20. She isn't got fired from her 6th job this year two months ago and I'm having to work overtime at Target. I'm paying bills and for her schooling (she's failing all her classes) and child support. My ex has sole custody of our 4 year old son. I get him every Wednesday and every other weekend and rotating holidays. So there's a 16 year old boy who works with us and he was walking home. We're in a pretty ghetto area and there was a shooting Saturday. I why he was walking because his mom always picked him up. He blushed and whispered that the car got repossessed. So I asked my boss if I couldn't clock out early and give him a ride. He said of course. In the car he said how the car getting repossessed was his fault because he didn't get paid soon enough to pay it off. I said I'm sorry and asked where his mom is working and he said she doesn't. I pulled a 20 out if my purse and gave it to him and said if he's okay with waiting an extra 30 minutes everyday I'll drive him home. I told girlfriend about what happened and she got mad. She said I had no business being in a car with a horny teenager and giving him our hard earned money when she has to pay for her next semester. I told her it was 20 bucks. Maybe I was wrong to give it to him but I didn't like how she was talking to me. She ended up slapping me and calling me a dumb bitch.