I think the only people who will know if you can afford the payment is you and your boyfriend. Just because you get approval for a particular mortgage doesn't mean you can afford it.
Sit down and work a budget out including everything you guys pay for, put into savings, and make sure you include for things you may or may not have to pay right now, such as utilities.
One thing you can do prior to when you have to pay the mortgage is set aside the extra money you will need for the payment and see if you can do this, or if you feel like you don't have enough money by the end of the month.
If you're able to set the money aside with no problem, then you're fine. But if you feel stressed, then it's too high.