Why is the spark I used to feel with him gone?

For around five months I pursued this boy. He had been in a miserable relationship with his girlfriend who controlled his life. Whenever I used to look at his picture or hear his voice I used to feel butterflies inside. But now its just...comfortable I guess. I want that spark back. I can't leave him. He has significant family issues and if I left it would make his life horrid. He says he loves me, and I used to think I loved him. I mean I know I love him, but I want to feel a bit of a rush. I know this sounds so shallow but if anyone could offer me advice, it would be much appreciated.