Children are a bit like stuff - they expand to fill up all of the space available :o
But I do think with my first, I was really quick to jump to his every need, rather than putting myself first. Yes I read a lot of articles about "filling your own cup first" etc but I didn't really follow it because I didn't feel like my cup was empty. I was just so obsessed and entranced with him. Which is fine - it's hormonal and instinctive, it's totally normal. But thinking along the "expanding to fill up the space" metaphor - probably if I'd actually set an intention to carve some space out for me and stuck to it, that might have been a good thing to do.
I had a more involved partner the second time around. It was immensely good for my mental health to just check out sometimes and leave the baby/toddler with DH. Whether that is going out for the day/evening, going for a nap, going to sit down and read in another room, or saying you do dinner, I'm too tired etc. And to be fair, he would do these things spontaneously as well. When you are doing everything, it's way too much.
If the baby is happy chilling out just leave him be for a little while. It's lovely to cuddle them. It's nice for them to have some space as well. Once they start getting into rolling, crawling, playing - make sure you give them space to explore and do their own thing and get frustrated and solve their own goals. Don't rush to fix every situation for them. Janet Lansbury writes very nicely about this. I found it really good at about 4 months and then I forgot all about it and ended up with a really entertainment-dependent toddler 
It's worth figuring out if you're too quick to say no vs too quick to say yes. Most of us lean one way or the other. If you are too permissive, look up PET (Parent Effectiveness Training). If you lean towards too authoritarian, look up gentle parenting. (If you're not sure which of these you are, the title you are drawn to is a big clue - read up on the opposite one.) There is a lovely middle ground which is collaborative and respectful where you work with your child, but they neither walk all over you nor are intimidated by you.