"I..."

He couldn't quite say it to Rosita. He talked around it and then let her make an inference which had become quite obvious. Here and now, he's afraid. He's actively touching Jacob. However he responds to the truth, Astarion will feel it.

But maybe he should feel that. Whatever shock and revulsion Jacob feels on learning what his lover is capable of. He deserves it.

"During the breach, I - forced myself, on someone else."