Sounds like you want your cake and eat it too... You cannot have the close physical intimacy of your boyfriend with the emotional/mental closeness of your ex... sooner or later... your boyfriend will need the emotional/mental closeness, and your ex will want the close physical intimacy.
It's unfair for both... you're disregarding your boyfriend's feelings and stringing your ex along.
Overcome your selfishness and either be a good girlfriend and put some distance between you and your ex --- for his peace of mind.... or.... cut your boyfriend loose and reconnect with your ex. It's up to you who you pick... but your selfish desires for both is only going to hurt everyone involved. You, included.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen