This is, in my opinion, something which a simple spell cannot accomplish, if anything at all can. At the very least, it would require openness from the other person, a very thorough practice of readily triggering lucid dreams with very strong control, and the ability to expand your awareness to a place outside your body (whichever type of journeying you may choose to call it).
If you want to see the dream he had, that is not so likely; it is now just vague bits of a subconscious experience stored in his memory.
But with a lot of hard work, a lot of meditation, and practice, you may be able to share a dream. It will be a personal gnosis of yours, if you believe you have but your lover insists the dream was different. It will be a shared gnosis if you both concur on the contents of the dream, whatever it may be.
It is my own opinion that this is not something which is at all likely, considering what a dream is, and how dreams happen.