Cheating

So I have this feeling that my SO of 10 years is cheating and it kills me to think so but I really feel as if he is. 1st our intimacy is non existing the last time we did anything was valentine's day and before that was sometime in 2016 we have been together since we were 19 and this has been going on for at least 2 years. Then last night ok this is going to sound stupid but he forgot he had his blue tooth on and the speaker is in our room and he was in the down stairs bathroom and it went off he was watching a snapchat of a girl. She giggled and said I'm snapping you. Then his Bluetooth turned off so I don't know what else it said. He stays up till 4 or 5 am everyday "watching" dragon Ball z but I have seen him on his phone instead of watching I don't know what he's doing on his phone I can't see it but I just get this weird feeling. Please I don't need anyone telling me to leave him or bashing I just needed to tell someone I have no real friends I could talk to and I don't want to start telling my sister she would go crazy on him. Do I sound crazy or do I sound like I could be possibly right to start investigating as much as I can first.