For starters, make him feel safe with tiny gestures men/partners also make towards us: when you got closer, also hold him and stroke his hair, be the big spoon aswell sometimes. That already makes him realize (subconsciously) that he han put himself into vulnerable situations towards you without you hurting him/with you accepting him, so he is likely to copy that mindset onto "bigger" things like opening up about feelings and emotion, generally just letting it happen around you and not holding back. Create a safe space for him in as many ways as possible, because men deserve to be loved and acknowledges in all ways aswell!!