Can a landlord have a lease signed with you and then turn around and say that he doesn’t want to rent to you?

If you have a lease, that lease, as a contract (that's what leases essentially are) is enforceable. Assuming that you are in compliance with your obligations, the landlord must honor his. That's not to say he can't offer to give your money back and tell you he'd rather not rent to you--but he can't back that up legally. If he wants you out, he'll have to make it worth your while--come up with some offer that gets you to agree to vacate. Of course, the landlord is under no obligation to re-rent to you when this lease is up (unless the lease itself contains some sort of automatic renewal term), so the very day after the lease is up, if you're still there, the landlord can begin eviction proceedings. Also, having personally lived through some bad landlord-tenant relationships, the next 6 months can be trying if the landlord really doesn't want you there; if possible, given your situation, working out something you can both live with--e.g. that you'll move out in 2  months, say, without any futher liability--may be in your interest.

No, it is not legal.  If you have a valid lease agreement that has been signed by both parties then you have a contract for the premises and he can not breach that contract.  The question here is what do you want to do?  Do you want to move in and enforce the agreement as against him?  Do you have a signed copy of the lease agreement? Did you pay the entire 6 months up front or just the first month and security?  Really, it does not matter as long as it is signed by both parties.  I would let your landlord know that you wish to abide by the contract that you entered in to and you are asking that he do so as well.  Otherwise you may have to take him to court to enforce it.  Good luck.