It's tough when a parent or someone you know says one thing but then acts a different way when faced with a certain situation. It seems like your mom is more uncomfortable than she thought or let you believe when actually faced with the fact that you are having sex or fooling around with your boyfriend. Maybe she didn't realize how she would deal with the issue until she walked in on the two of you, and she's a bit freaked out by the reality of it.

It sounds like you need to give your mom a bit of time to process all this. Maybe, if she is really not talking to you at all, you can write her a letter asking her how you and she can deal with things and how you can get her to talk again. She may be angry and contradict herself about supporting your choice--or she might be fine. If she is still angry, find out what's changed for her and see how you can resolve things together.

Also think about where you and your boyfriend can go if you plan to continue seeing each other and/or have sex. Be considerate of your mom's feelings and space.