Meet my boyfriend's kid in a few hours

Guys I posted last night about finally meeting my boyfriends 14 year old son. I'm just nervous because his son does have trauma. His step dad killed his mom and he had to witness it. I asked for advice if I should give him something and i did ask my boyfriend and he said it doesn't need to be a big gift. A snack is fine. So I got a few of snacks my boyfriend said he would like. My boyfriend did warn me that when it comes to him dating he does get jealous. He assured me he won't be disrespectful or anything towards me. He just starts to act very immature and whining and clingy towards him and his therapist said that was normal. So my question is does anyone have any experience with this or kids with trauma. I'm obviously going to follow my boyfriends lead. I love him and want to his child's approval. Not to replace his mom of course. Just to be there.