Like "oh, so you have mixed feelings about that?" And so on.
Looks like he is looking for a fight. Don't JADE, don't pick up the gauntlet!
Do not beat yourself up for being open and taking a risk you did nothing wrong. Just because he is now using "mixed feelings" as club to beat you over the head. It is just his newest tool and luckily it is nothing very personal.
Having mixed feelings about some things is normal but is a concept that is very hard to swallow for a pwBPD who strongly prefers a more clearer black and white view of life.
Mixed feelings is dialectic and an important stepping stone to feel comfortable with Grey. We love our partners a lot and we dislike quite a bit about their behavior and we are ok with that. Well, our partners struggle with such realities a lot.
Him using "mixed feeling" in inappropriate ways to hurt you is also a sign of immaturity (surprise) as is might well be insecurity of how to relate to the concept. It might be worth for you at times to take more dialectical positions (avoid the term "mixed feelings as it is for the time being tainted) as he ultimately needs to become more comfortable with the concept.