To lie is human, not getting caught is divine. You are a liar if you were caught lying, you'll be a saint if you lie without being caught. The perfect boyfriend can be the perfect boyfriend or he could very well be someone who were yet to be caught lying. If you want to lie, make sure you know how to lie properly. The least that you could do is to cover your tracks. Telephone records, sms, browsing history, please learn to clear them. Tools>Option>History>Clear. It's freaking simple.
Don't shit where you eat. If you want to sleep with someone else, don't sleep on the same bed your boyfriend is going to sleep, no matter how impossible it is for him to find out. You never know when the next guy might just decided to cling to you instead, then you'll wish you never brought him home. Life has a way to turn it all against you.
Lying is a spiral of despair. Once you lied, you have to make up more lies to cover it, which is where people found out that you lied. Instead, choose not to tell the whole truth instead. Did you sleep with you him? I wouldn't dream of sleeping with him! See the catch here, you didn't dream to sleep with him as you have already slept with him. Technicality.
Lying is a fine art. It is easy to learn but hard to master.