Ha ha actually my girlfriend loves it when she can here my heart beat, It is because I know I really have feelings for her and when I have her in my arms I never want to let go of her and I love her and that makes my heart smile/ my heart beat faster and louder so she can feel it. These are the reasons my girlfriend can feel my heart beat and I bet your bf has the same feelings and that's why you can feel his :) I hope this was helpful for you:)
