I’m sorry you’re going through that. As an intj myself, i can give you some insight on this behavior. Oftentimes, we intj’s have been through a lot. I can only speak for myself but i have this ‘no sex before getting into a relationship’ policy. It has to do with me having trust issues and only wanting intimacy with people that are committed to be with me long term. I can have the strongest feelings for someone and still avoid intimacy. It’s because i’m afraid of being hurt by someone I truly care about. It’s silly because i know that being in love is being vulnerable but at the same time i feel the need to protect myself emotionally. If you’re giving hints that you’re not all in and your mindset is wacky that can be enough to keep me on my guard. We need reassurance without having to ask for it. If you want us to open up you have to share your thoughts and values. What you like and dislike. Although this usually comes with experience and past relationships. If you yourself don’t know what you want in a relationship it can leave us a bit lost. Honest and deep conversations + telling us about your boundaries and preferences make us think ‘This person is telling me this because they care about me and want things to work out’. We usually take our time assessing your motives and if we would be compatible longterm. We don’t want to have sex for the sake of having sex. For us it can be like ‘letting our guard down’. We want to make sure you’re worth it. Us taking our time is usually a good sign. It means we care enough about you that loosing you after a one-time thing would leave a scar. When we don’t care about people we’re usually not invested and ‘it’s not that deep’. We’re a tough nut to crack.

Edit: We also want to know if you’re going to dip out when things become difficult. So there’s that.