Is he cheating or am I crazy?

Sa
Hi ladies!
My man been acting distance. He haven't call me once his gf, 6 months into relationship. Friday night we had sex. Saturday I work and he hung out with his friends. Saturday night j meet up with him and his friends after a bday party with the girls club night. Girl! I saw a hickey on his neck! His friend swear nothing happened but  I knew I didn't have it to him on Friday night I was sober!! When I confronted him he said "don't you remember you ALSO gave me a hickey like 2 months ago, you never remember anything, this is just another one you gave me on Friday when I stayed over" 
I mean ladies, I know what I do in bed, and if I did gave him a hickey I would admit and not freaking out like this!! 
Everything is just kinda gather together I asked him why he been so distance he said "I've been stressing over work on that new position"