Did he cheat?

So my boyfriend and I have been together about 7-8 months, he moved to a new city with me. Lived with me in my apartment for 2 months while looking for his own place. The other night we were hanging out and both had work the next day so he left around 11pm (ten minute walk home). The next night he is sleeping over, I see an email for a "lyft receipt" from 2am the previous day. I confront him about it and he refuses to open it saying it's nothing. Guarantees me time and time again he's not cheating on me. He said I should trust him. I can't help but feel incredibly suspicious and crazy that he downloaded grindr and went to meet someone that night.