Why does the one person that you are asking to work WITH you never believe that you will take negative action, forcing you to prove what you said would happen (especially if they vocally acknowledge but physically refuse to make the effort in order to help make things better)? As children, many are warned that they will be spanked if they do not obey their parents/parental figures. A lot of children refuse to obey, knowing that the parent is simply using a “scare tactic” to make them behave the way that is desired from the other.
Relationships (of any kind) always end up going back to the “high school” mentality when an argument arises. The measure of maturity is how we choose to handle this argument; do you want to go back to “well, you said/did this first” or would you rather adhere to the rational way and admit your own fault in the argument without blaming the other person or something/someone else for your actions (or lack thereof). In life, it is our choice of how to handle things that makes us adults. Another person can not make you feel guilty, it is an emotional mind game and age does not matter; guilt will grow with you.
That is, unless the guilt you feel is unfounded and just a silly teenage game someone plays to force you into feeling shameful for something that you need not feel at fault. The true test of becoming an adult is whether you will play the silly mind/emotional games you did as a child/teenager.