I'm going to sleep with someone while seeing someone else.
Do you think you can get away with it?
Yes, women all like and trust me because they think I'm nice.
It is wrong to see multiple people at once if they don't know. If they find out you could be dumped by all parties involved and end up alone.
So what? Do you think that bothers me?
If you don't care if neither of them want to see you anymore, it might be best just to end the relationships now so as to avoid hurting them any further. If you want a strictly sexual relationship, there's nothing wrong with that, but you need to be up front about it so everyone involved knows what to expect. Cheating on your girlfriend is cruel and extremely hurtful.