Please help me

Hi everyone. I have developed feelings for a guy who is in a relationship. He and I are really close friends and we talk all the time. He tells me that his current girlfriend doesn't respect him or his opinions and makes decisions specifically to hurt him. Normally, I wouldn't trust these accusations, especially coming from a guy, but he's shown me the messages. She is studying abroad and requested to have an open relationship. When he found out that she had hooked up with someone else it absolutely crushed him but he didn't say anything to her about how upset he was.  He says that he loves her anyway and that she is "the one" but I can't help but feel like he deserves more than this. I want him to be happy but I feel myself falling for him harder and harder each day. Seeing him hurting, knowing she's sleeping with other guys, breaks my heart and I find myself longing to help him. And I know I could never do anything to intentionally hurt him. Do I tell him about my feelings or just leave it alone? I don't know what to do, I don't want to cause any trouble