Out of respect to your son, be intimate when he is asleep (as u did in this case). Really can't control him getting up at night, but maybe while your son is home try to be more aware of how loud you are :)
We single mom's need to be a little more aware of our child's feelings, considering we have a man in our home that isn't the child's father. Its respect we need to show them. Also be up front and honest with your son. Talk to him as a friend and as a parent. Have him express to you his feelings and address them. His feelings should be priority over your own sexual relationships with another man.
I am teaching my son to express himself now that mommy has another man in my life. I have been single for 6yrs and my son was the only man in our house. Now that I am active in a relationship for the first time, we both (my boyfriend and I) make sure my son is not left out and is always welcome to express his issues or concerns freely. If he isn't happy with something he is allowed to speak his mind. For example..i was in my truck as passenger in the back sitting beside my truck. The boyfriend was driving. I leaned forward to give him a neck massage. My son asked me what i was doing. When I told him i can tell something bothered him. I asked him what was wrong, he immediately told me he was jealous that i was touching my bf. So immediately stopped and cuddled with my son in the car the entire ride home.
As a single parent, our children do come first...at least in my life, my son will and will always be the man in my life. Therefore he WILL ALWAYS come first. Regardless of how long of a relationship i am in. The man in my life will knows this immediately upfront.
So be a tad more aware...communications is KEY. And speak to your son stating its not polite to ease drop on you during "your time" which can be established with him. Like a "mommy time" curfew :)
Hope that helps!