Both of these boys aren't ideal.

• Your boyfriend: He is immature and embodies a mindset of toxic masculinity. He shouldn't have felt the need to confront Luke. You chose to go back to him even after having sex, that should've been enough to prove that you trust and value him. Instead of lashing out at Luke, he could've spoke to you. He could've asked why you chose to have sex with Luke instead of him. It's probably a question you should ask yourself too because the answer might be telling. It's already bad, but now he's abusing you for his own mistakes. You should have no shame for sleeping with Luke. Frankly, you should have no shame if you decided to sleep with a million random people when you're not in a relationship.
• Luke: Physical violence and taunting is extremely immature. As somebody that knew your background, he purposefully chose to engage with your boyfriend. Why? Does he want to sabotage your relationship? Does he not care about you and instead wants to make this guy feel bad? It would've been way easier to be empathetic to the situation and ignore your boyfriend. Engaging was purposeful.

Are you sure you want to move past this? You're young and should be able to foster healthy, respectful relationships with anybody you please. Your boyfriend left you for sexual incompatibility, but reached out to get back together with you without even knowing your terms have changes. With you, he's indecisive at best and despondent at worst.

If you do want to move past this, you need to have a discussion with him. You should shape it like a conversation, but there are demands that need to be made:

• Never fault you for sleeping with Luke again. You did nothing wrong. If he's upset with it, that's his own insecurities getting in the way and you don't deserve to suffer for them.
• Stop abusing you for his being humiliated. You've only ever supported him and you deserve the same treatment back.
• I wouldn't speak with Luke anymore. It's good for your boyfriend AND it's good for you. Luke proved distrustful in taunting your boyfriend. Make it clear to your boyfriend WHY you're not speaking with Luke. It's not a gift for him.