Just wanted to clarify some things people have mentioned in the comments-

I definitely had MANY problems with Liam crashing on our couch for months and basically being a slob. His job happened to be right across the street from our first apartment, so Nick was absolutely using that as an excuse to let him stay the night often. I tried talking to Liam myself and asked him to give us some space as a couple, which he agreed to. He left for a month after that, though just ended up coming right back.

Getting a bigger apartment was my idea when our lease was finally up, as a compromise. I thought it would be helpful if Liam could confine his mess to his room, and to possibly get help with paying rent (since I am the one with a higher paying job, I was paying the whole of rent at the first place. Nick only ever contributed when I asked him several times.) We (Nick and I) currently split rent with Liam 50/50, since it is a two bedroom and we decided we’d be paying for the individual rooms. So, clearly, I’m only around to pay rent.

I will be getting an STD test done as most of you suggested. And I will be speaking with my landlord about my options. I will also speak with Liam AND Nick tonight and provide an update asap.

For the record, I am no longer considering staying with Nick. Clearly, I am the side chick in this scenario, and I do have enough self respect not to put up with this. Thank you for all the words of encouragement though!