How do I (20F) set boundaries without feeling bad?

r/

Basically the title. For some reason I don’t find an issue setting boundaries early while dating, or with friends/other people. But being in a committed relationship for 2 years (that I do feel stable in for the most part, and really happy), I feel myself letting go more and more of my boundaries. It makes me feel like I’m being a doormat, and it makes me feel like my partner (21M) is less willing to put in effort generally, or during fights less willing to back down, because he knows I’ll always come back around. Sometimes even when we’re intimate.

When I do communicate I always do it gently, but we both care so making him feel bad makes me feel worse. He never intentionally tries to make me uncomfortable, but I also think in his toxic ex relationship he would try way harder to please her, which makes me feel pretty sad.

I unintentionally equate being firm or colder as being a b*tch (not in a derogatory way, he’s never called me that ever), while also believing men turn into puppies when a woman doesn’t give them as much attention.

Tl;dr : How do I set boundaries without feeling bad? Does being colder mean that guys are willing to put in more effort in relationships? How do I become more comfortable in expressing my dislikes and not feeling bad the other person feels bad, for doing something uncomfortable in the first place?