We have been together for over 6 years he wasn't very experienced when we got together and I encoraged him to explore his sexuality we were very happy and enjoyed experimenting with each other but now he sneaks off or waits until I'm asleep to pleasure himself but won't have sex with me what am I supposed to do

He's upset about something... or might think you are trying to get pregnant and he isn't ready for that. Have you actually asked him yet?

Talk to him.

Have you asked him what is going on? How long has it been going on?

You can look at what is going on your lives that might have him wanting a quick release rather than having intercourse. Is he stressed, tired, worried, etc. Are there any health or medical/medicine problems? Has anything changed such as where you are living or if you live alone?

How do you know he is 'pleasuring himself'? Keep in mind that people can look at porn/erotica and not masturbate.

He could be going through a phase of not being fully interested in sex. It can happen for both men and women.

Talk to him and find out what is going on in his mind. It will give you a place to begin even if it doesn't answer all of your questions.