What do you do when you start to sense a partner is having thoughts of ending the relationship?

My partner of 1.5 years (first poly relationship) has started seeing more people, been harder to arrange date nights with, and started criticizing me for what seem like kind of small things. The last time he was over he asked if this was our last date...when I said no and that I thought that was a weird question because I had literally just agreed to meet meta, he was kind of sarcastically like "oh yeah that'd be totally weird".

But then, on our last date he really opened up and shared parts of himself he hadn't previously and he said he wanted to go back to our previous schedule of meeting on a regular basis. Told me he loved me, etc etc...

I'm just getting so confused and I hate constantly asking for reassurance because it makes me feel really needy. I dunno, I know yall are not mind readers but wtf

Eta...we've been through A LOT lately and are kind of at a turning point where I think we probably do need to either choose to stay or go.

Also...he's all over the place on a lot of stuff. Like, I asked him to talk with me about the future of our relationship and he responded saying we could talk about sexual desires. Then a couple dates later he wanted to talk about relationship future and reflection. I just never know how to gage things...