I think partner is tired of me

I need some advice asap. So I’ve been dating my partner for almost 6 months. I also have 3 other partners including a nesting partner. So, partner of 6 months has ALWAYS been close to me, texting me about everything and I do the same with him. To the point of healthy obsession lol. BUT as of the beginning of January he has begun acting different towards me. Not texting me for hours, the effort seems different etc. in December him and I spoke of legal marriage even down the line (obviously not right now) but just so you can get a view of how close we are. As of Monday he claimed he was exhausted and brain fatigued (he has several metal illnesses as do I) he put his phone on dnd and has texted me about twice a day since Monday and phone still on dnd. This is NOT his pattern whatsoever. NEVER. However, he does not work, lives with his parents. So this isn’t a job tiring him out. He leaves me on read now but I see him answering his other partner on facebook comments. He hasn’t say good morning or goodnight in two days. Tomorrow will be day 5 of this. Around the time he began acting different to me he met a guy (the partner he answered on facebook comments) and said guy is in a relationship with two other people (the 3 of them date as a polycule I believe) so my partner is with all 3 of them, two live out of state and one 2 hours from him. Him and the guy were supposed to go on a date last Saturday but ended up canceling due to weather which he NEVER told me about the date,I found out myself through the grape vine. He said he kept it from me because we haven’t see each other since November and I’ve been basically begging to see him irl a lot (we live an hour apart) and he didn’t wanna upset me. In the past two weeks we have been in about 3 arguments due to me wanting to see him irl (this is a love language for me and I absolutely MUST see a partner irl atleast 3 times a month) I have apologized every time I’ve gotten upset. He also took back the marriage ideas (legal marriage) and says he can never get married legally due to seeking disability. This isn’t what he said in December. I’m so confused, what should I do?