Interpret my situation!?

[Jen P]

I have a guy friend, whose girlfriend is majorly jealous of our relationship and wants us to stop being friends. But we can't. He would call me every night and ask about my problems and I would ask about his. Whenever I wasn't able to answer his calls, I'd tell him the reason why: because I get grounded a lot. He would tell me that he's worried about me and that I shouldn't get in trouble because of him. I keep trying to stop answering some of his calls because his girlfriend gets jealous but then he tells me never to ignore him and that he'll deal with his girlfriend himself. I tell him "but your girlfriend yells at you for defending me." And he tells me "what kind of a brother would I be if I didn't defend my sister?" (We call each other brother and sister, because we're just that close). He would at first pretend he didn't see me whenever his girlfriend would be around, then before he or I left the room, he would look over and stick out his tongue or smile to let me know he isn't ignoring me. At night we'd talk about how and why his girlfriend is jealous and how we can assure her nothing is going on between us. We'd try and not talk to each other but after a day or two we'd miss talking to each other too much and text each other again. We make each other feel special and still remember the first day we met clearly. We had little crushes on each other and now we're close close friends, talking in our native tongue to each other like we're twins! I think I even care about him more than his girlfriend does. Right now, we're trying not to talk to each other again, but I miss him already. What do you guys think of our relationship? What is my next move?