I guess I should be more careful about what I say.
Why should you be more careful in what you say?
I don't want to lose my partner, who I care about deeply and who always understands and supports me. I need to watch my words.
It's good to think before you say something. It's good to think about your partner and their feelings and what you say first.
I know but this is going to be harder than I thought.
It usually is easier to say than to do. Give your thoughts some time to process and mull them over patiently. Try writing down some feelings into a journal and explore your inner thoughts so you can better express them.