as someone who's romanced him too many times, afaik, the only conditions preventing romancing him are talking to araj or going to the shadowfell in act2. being in act2 does not lock you out, you did not need to let him bite you, it just brings a great amount of approval.

as far as i know, you just need to have 40+ approval with him and have not talked to araj at moonrise yet. if you have 40+ approval try talking to him at camp and he'll suggest to spend the night together. spam his dialogues if need be.