deceiving guys

I met this guy about a month ago and he's really into me, im making him take it slow.... so like we haven't even kissed... he's perfect and loves me but i dont feel attracted to him. anyway, a week ago i caught up with an 'old flame' and have been sleeping with him for the last week, thinking about going out with him. I feel bad for not telling the guy i met first about this, i just dont know how to break it to him. But i have a massive love bite on my neck right now and if i see the first guy in person he'll know exactly what i've been up to.... i dont want him to be upset, so im not going to tell him the truth. and both guys have no idea about each other.