Applying for a TS clearance while living with undocumented boyfriend

I recently was selected for a position that requires a TS clearance. At least, from my part, I have no issues at all. However, the same may not be true for my boyfriend. I will try to include info that I think will be relevant. My boyfriend who is from Brazil arrived in the States when he was 20yo (he is currently 23yo). His family lives here, they are legal residents, and he even has native-born American siblings. He entered legally in the country with a tourist. His visa expires in 2024 but he already exceeded his allowed time stated in his I-94. We have been dating for almost two years already. Since almost a year already he has practically been living with me in my apartment (I own the apartment – paying mortgage). However, he pays all his bills and even help me with expenses. He doesn’t want to live with his family (he can live at his own), has a stable job, speak very good English, he is already very adapted to the US culture, and he even has a NY state ID (NY allows people with good record to have a state ID providing that have proper ways to demonstrate identity and payment of taxes).

Based on what I have read, his status may be an issue. I’m trying to find out to what extent this is the case and find ways to mitigate any possible issue. He can and has no problem in moving out (either way, I’m and will be 100% honest in my application and mention my relationship), if that helps with my clearance.

Since it is just a matter of time (couple of weeks) until I receive the notification to fill out the SF86, considering that I was already considering marry him, I don’t know if I should just mention that or even marry him right now.

I’m just trying to explore my alternatives and make the best decision for our future and my dream job… and of course improve my chances of obtaining the clerance with no so much trouble

Any relevant constructive opinions / helps / advice would be greatly appreciated it.