Is my boyfriend gay?

Recently my boyfriend of 2 years (he’s 31 I’m 25) we’ve been having some rough trust issues. I decided to snoop thru his phone which I’ve never done and although I didn’t find what I thought I would – I feel worse. I saw messages and photos and videos he was exchanging on WhatsApp with another man that he met on Grindr. Now my bf has never dated a man. Or neither is he bi. (That I know of) but now with this new found information I don’t know what to do. We’ve been having a rough patch so if I dump him it won’t be out of the blue but I’m just so shocked right now. Help.