relationship struggling after baby

My fiancé and I have been together for 11 years and had our first ban in January. We got engaged in December and no, I do not consider that a red flag or anything as I’m not really into getting married and we got together at 17 years old so there was genuinely no rush. With that being said, we are struggling so bad. When I was pregnant we would have the occasional argument but nothing crazy. For the most part he took really good care of me. Especially towards the end. He was my rock during labor and postpartum. I was terrified I’d get PPD and tbh I think he’s the reason I didn’t.

I would do the middle of the night feeds and he’s do the 5 or 6 am feeds. When I’d wake up he’d have everything laid out for me. Pumps, vitamins, water, burp cloth and boppy etc. he’d shower before I woke up that way I could shower when I woke up and he’s clean up the house while I showered. He was able to take off 9 weeks through PFL and It was so nice to have him there and we were as close as ever. Then he went back to work and of course he wasn’t able to do or help as much as before but I understood and we were still good. When I went back to work and we were few both busy with our schedules is when I felt our relationship really go downhill.

We argue all the time, he also has a lot going on in his personal life with family etc and has been struggling with depression and I’m trying my best to be there for him but I feel like our relationship is falling apart and I don’t know what to do.