What is the adjusted cost base refer to in case of a spousal separation when i was bought out? The original purchase price was 305k, and i was bought out for 110k.

Assuming the house was bought between you and your ex and you each had a 50% share of the house.

In this situation, your portion of the original purchase price would be 305K x 50% = 152.5K. And you would be reporting a proceed of 110K.

Unfortunately, if this was your principal residence for all the years, you would not be able to claim the loss. If there was any years where it is NOT your principal residence, then you would be able to claim a portion of the loss.